Chapter 15: Images

Parameters	Details
src	Specifies the URL of the image
srcset	Images to use in different situations (e.g., high-resolution displays, small monitors, etc)
sizes	Image sizes between breakpoints
crossorigin	How the element handles crossorigin requests
usemap	Name of image map to use
ismap	Whether the image is a server-side image map
alt	Alternative text that should be displayed if for some reason the image could not be displayed
width	Specifies the width of the image (optional)
height	Specifies the height of the image (optional)

Creating an image

To add an image to a page, use the image tag.

Image tags (img) do not have closing tags. The two main attributes you give to the img tag are src, the image source
and alt, which is alternative text describing the image.

<img src="images/hello.png" alt="Hello World">

You can also get images from a web URL:

<img src="https://i.stack.imgur.com/ALgZi.jpg?s=48&g=1" alt="StackOverflow user Caleb Kleveter">

Note: Images are not technically inserted into an HTML page, images are linked to HTML pages. The <img> tag
creates a holding space for the referenced image.

It is also possible to embed images directly inside the page using base64:

<img src="data:image/png;base64,iVBOR..." alt="Hello World">

Tip: To link an image to another document, simply nest the <img> tag inside <a> tags.

Choosing alt text

Alt-text is used by screen readers for visually impaired users and by search engines. It’s therefore important to
write good alt-text for your images.

The text should look correct even if you replace the image with its alt attribute. For example:

<!-- Incorrect -->
<img src="anonymous.png" alt="Anonymous user avatar"/> An anonymous user wrote:
<blockquote>Lorem ipsum dolor sed.</blockquote>
<a href="https://google.com/"><img src="edit.png" alt="Edit icon"/></a> /
<a href="https://google.com/"><img src="delete.png" alt="Delete icon"/></a>

Without the images, this would look like:

Anonymous user avatar An anonymous user wrote:

Lorem ipsum dolor sed.

Edit icon / Delete icon

To correct this:

• Remove the alt-text for the avatar. This image adds information for sighted users (an easily identifiable icon to show that the user is anonymous) but this information is already available in the text.1
• Remove the “icon” from the alt-text for the icons. Knowing that this would be an icon if it were there does not help to convey its actual purpose.

<!-- Correct -->
<img src="anonymous.png" alt=""/> An anonymous user wrote:
<blockquote>Lorem ipsum dolor sed.</blockquote>
<a href="https://google.com/"><img src="edit.png" alt="Edit"/></a> /
<a href="https://google.com/"><img src="delete.png" alt="Delete"/></a>

An anonymous user wrote:

Lorem ipsum dolor sed.

Edit / delete

Footnotes

1 There is a semantic difference between including an empty alt attribute and excluding it altogether. An empty alt
attribute indicates that the image is not a key part of the content (as is true in this case – it’s just an additive image
that is not necessary to understand the rest) and thus may be omitted from rendering. However, the lack of an alt
attribute indicates that the image is a key part of the content and that there simply is no textual equivalent available
for rendering.

Responsive image using the srcset attribute

Using srcset with sizes

<img sizes="(min-width: 1200px) 580px,
 (min-width: 640px) 48vw,
 98vw"
 srcset="img/hello-300.jpg 300w,
 img/hello-600.jpg 600w,
 img/hello-900.jpg 900w,
 img/hello-1200.jpg 1200w"
 src="img/hello-900.jpg" alt="hello">

sizes are like media queries, describing how much space the image takes of the viewport

• if viewport is larger than 1200px, image is exactly 580px (for example our content is centered in container which is max 1200px wide. Image takes half of it minus margins).
• if viewport is between 640px and 1200px, image takes 48% of viewport (for example image scales with our page and takes half of viewport width minus margins).
• if viewport is any other size , in our case less than 640px, image takes 98% of viewport (for example image scales with our page and takes full width of viewport minus margins). Media condition must be omitted for last item.

srcset is just telling the browser what images we have available, and what are their sizes.

• img/hello-300.jpg is 300px wide,
• img/hello-600.jpg is 600px wide,
• img/hello-900.jpg is 900px wide,
• img/hello-1200.jpg is 1200px wide,

src is always mandatory image source. In case of using with srcset, src will serve fallback image in case browser is
not supporting srcset.

Using srcset without sizes

<img src="img/hello-300.jpg" alt="hello"
 srcset="img/hello-300.jpg 1x,
 img/hello-600.jpg 2x,
 img/hello-1200.jpg 3x">

srcset provides list of available images, with device-pixel ratio x descriptor.

• if device-pixel ratio is 1, use img/hello-300.jpg
• if device-pixel ratio is 2, use img/hello-600.jpg
• if device-pixel ratio is 3, use img/hello-1200.jpg

src is always mandatory image source. In case of using with srcset, src will serve fallback image in case browser is
not supporting srcset.

Responsive image using picture element

Code

<picture>
 <source media="(min-width: 600px)" srcset="large_image.jpg">
 <source media="(min-width: 450px)" srcset="small_image.jpg">
 <img src="default_image.jpg" style="width:auto;">
</picture>

Usage

To display different images under different screen width, you must include all images using the source tag in a
picture tag as shown in the above example.

Result

• On screens with screen width >600px, it shows large_image.jpg
• On screens with screen width >450px, it shows small_image.jpg
• On screens with other screen width,it shows default_image.jpg