Table Of Content

HTML Images Tutorial

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1- Attributes

The <img> tag helps you display an image on the page. The list below shows you some attributes of the <img> tag.
Attribute Value Description
src URL Specifies the URL of an image
alt text Specifies an alternate text for an image
width pixels Specifies the width of an image
height pixels Specifies the height of an image
crossorigin anonymous
use-credentials
Allows reading image data from another website to work with Canvas on the current website.
ismap ismap Specifies an image as a server-side image-map
sizes   Specifies image sizes for different page layouts
srcset URL Specifies the URL of the image to use in different situations
usemap #mapname Specifies an image as a client-side image-map
Note: This list does not consist of the  align, border, hspace and vspace attributes. The reason is that these attributes were introduced in HTML4.1, but they are no longer supported in HTML5.

2- Src

The most important attribute of the  <img> is the  src, which specifies the URL of the image.
  • The src can be a relative path to the image file location.
  • The src can be a link to the image source.
<p>src='flower.png'</p>
<img src='flower.png' />

<p>src='../../_testdatas_/flower.png'</p>
<img src='../../_testdatas_/flower.png' />

<p>src='https://raw.githubusercontent.com/o7planning/webexamples/master/_testdatas_/flower.png'</p>
<img src='https://raw.githubusercontent.com/o7planning/webexamples/master/_testdatas_/flower.png' />
img-example.html
<!DOCTYPE html>
<html>

<head>
  <title>Image example</title>
  <meta charset="UTF-8">
</head>

<body>

  <p>src='flower.png'</p>
  <img src='flower.png' />

  <p>src='../../_testdatas_/flower.png'</p>
  <img src='../../_testdatas_/flower.png' />

  <p>src='https://raw.githubusercontent.com/o7planning/webexamples/master/_testdatas_/flower.png'</p>
  <img src='https://raw.githubusercontent.com/o7planning/webexamples/master/_testdatas_/flower.png' />


</body>

</html>

Base 64 URL:

The data of an image file is binary data which can be converted into a Base64 String by  Base64 algorithm.
Base64 String

iVBORw0KGgoAAAANSUhEUgAAAAUA AAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO 9TXL0Y4OHwAAAABJRU5ErkJggg==
 
The thing is, you are able to make a  Base64 URL:
Base64 URL

data:image/png;base64, iVBORw0KGgoAAAANSUhEUgAAAAUA AAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO 9TXL0Y4OHwAAAABJRU5ErkJggg==
 
For instance, the  <img> with the  src is a  Base64 URL:
base64-url-example.html
<!DOCTYPE html>
<html>

<head>
  <title>Base64 URL example</title>
  <meta charset="UTF-8">
</head>

<body>

  <p>Red dot:</p>
  <img src='data:image/png;base64, iVBORw0KGgoAAAANSUhEUgAAAAUA AAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO 9TXL0Y4OHwAAAABJRU5ErkJggg==' />

</body>

</html>

3- Alt

The alt attribute is used to display the alternative text to an image if the browser cannot display the image for some reason, such as the unavailable image source, the unsupported image format and so forth. Alt is short for Alternative.
Moreover, the Alt makes the image more accessible to the blind when they use Screen Reader, even though they cannot see the image, they are still able to read the content provided by the Alt.
The Alt attribute also supports the image collectors like Google.  Google uses alternative text as the key while it is trying to interpret what the image is about.
alt-example.html
<!DOCTYPE html>
<html>

<head>
  <title>Alt</title>
  <meta charset="UTF-8">
</head>

<body>

  <p><b>Img src='invalid source' alt='My Image'</b></p>
  <img src='invalid source' alt='My Image' />

  <br /><br />

  <p><b>Img src='flower.png' alt='My Flower'</b></p>
  <img src='flower.png' alt='My Image' />

</body>
</html>
Run the above example in Chrome browser like this:
Run the above example in Firefox browser as well:

4- Width/Height

The width and  height attributes help you specify the width and height for images in pixels. This allows the browser to readily provide the necessary space to display the image. However, if you do not specify these two attributes, the image which needs to be downloaded by the browser, will be set the size to display afterwards. As a result, the page layout may change during the process of loading the image
It is notable that in HTML 4.1 you can assign a value (can be a number in pixels, or a string), such as " 100%" to the width and height attributes. But in HTML 5 you can only assign a number in pixels to the width and height attributes.
width-height-example.html
<!DOCTYPE html>
<html>

<head>
  <title>Width/Height</title>
  <meta charset="UTF-8">
</head>

<body>

  <p><b>Img src='flower.png'</b></p>
  <img src='flower.png' />


  <p><b>Img src='flower.png' width= 30</b></p>
  <img src='flower.png' width=70 />

  <p><b>Img src='flower.png' width= 70 height=120</b></p>
  <img src='flower.png' width=70 height=120 />

</body>

</html>

5- usemap

An Image map is a technique for creating different areas on the image, each of which involves a link to a different page.
usemap-example.html
<!DOCTYPE html>
<html>

<head>
  <title>Image Map</title>
  <meta charset="UTF-8">
</head>

<body>

  <p>Move the mouse over the image surface.
    A few places on the image you can click.</p>

  <img src="languages.png" usemap="#image-map">

  <map name="image-map">

    <area target="_blank" alt="C" title="C"
          href="c.htm" coords="214,69,34" shape="circle">

    <area target="_blank" alt="JS" title="JS"
          href="js.html" coords="344,245,400,185" shape="rect">

    <area target="_blank" alt="Python" title="Python"
          href="python.html"
          coords="74,57,68,71,52,75,50,107,64,113,72,127,98,129,106,113,120,107,120,81,108,71,104,59"
          shape="poly">

    <area target="_blank" alt="Ruby" title="Ruby"
          href="ruby.html"
          coords="56,185,36,193,22,209,18,231,66,247,86,195"
          shape="poly">

    <area target="_blank" alt="Java" title="Java"
          href="java.html"
          coords="340,37,326,59,318,77,304,83,306,101,308,117,336,123,366,115,366,91,352,75,354,53"
          shape="poly">
          
  </map>

</body>
</html>
 
The website below is a tool to help you create <map> data:

6- ismap

The ismap attribute tells the browser that the image uses the  Image-map at the server side. When the users click on any part of the image, information about the focal point will be sent to the server as a Query-string.
<a href="/show-language-at">
    <img src="languages.png" ismap>
</a>
ismap-example.html
<!DOCTYPE html>
<html>

<head>
  <title>Image Map</title>
  <meta charset="UTF-8">
</head>

<body>

  <p>Move the mouse over the image surface.And Click</p>

  <a href="/show-language-at">
    <img src="languages.png" ismap>
  </a>


</body>

</html>

7- srcset, sizes

A friendly website must be adjustable to various devices with different screen sizes such as computers, tablets, phones and so on. Thus, the size of the image must be compatible with these devices as well.
The easiest way to make images suitable for all devices is to use the  CSS  max-width:
<img src="../../_testdatas_/tom-and-jerry.png" style="max-width:100%;">

srcset

The srcset attribute of the <img> tag helps you define a set of images as well as which situations they will be used.
For instance:
<img src="image300.png"
        srcset="image100.png 480w, image150.png 600w">
  • If the Viewport width is less than 480w, the image100.png will be used.
  • If the Viewport width is less than 600w, the image150.png will be used.
  • If neither of them happens, the image300.png will be used.
Use " w" to tell the browser the size of the image source.
  • Retina screen (available on high-end Apple computers) uses 200 pixels to display a 100w image.
  • The common screen uses only 100 pixels to display a 100w image.
With the same image, its size that you see on the Retina screen remains the same as on the common screen. However, the image on Retina screen is sharper.

sizes

The sizes attribute of the <img> tag allows you to define a set of media conditions as well as  indicates which image size is the best choice for each media condition.
<img src="image300.png"
        srcset="image100.png 480w, image150.png 600w"

        sizes="<media condition> <width>, <media condition> <width>, <optional default image width>"
/>


<!-- Example: -->

<img src="image300.png"
        srcset="image100.png 480w, image150.png 600w"

        sizes="(min-width: 900px) 1000px,
                   (max-width: 900px) and (min-width: 400px) 50em,            
                   ( not (orientation: portrait) ) 300px,            
                   ( (orientation: landscape) or (min-width: 1000px) ) 50vw,             
                   100vw"
/> 
vw is the abbreviation of the  Viewport Width. For example: 25vw = 25% of the width of Viewport;  100vm = 100% of the width of Viewport.
In fact, there are many issues for us to discuss the  srcset and sizes attributes, so they should be mentioned in a different article. If that is what you are interested, you can read the article below:
  • TODO Link!

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