HTML Images

HTML Images and Responsive image using the srcset attribute, picture element

Creating an image in HTML 

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.

You can also get images from a web URL:

<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 in HTML

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:

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.

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

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

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

Usage

To display different images under different screen widths, 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 another screen width, it shows default_image.jpg