Images, alt text, and speed
An image is content and weight. Without alt text, Google and a screen reader do not know what is in it. Without dimensions the page jumps. With a file that is too large, the visitor waits.
Three properties on every image
alt describes what is visible, it does not stuff keywords. A decorative image can have empty alt so a screen reader skips it. A service image needs a sentence: what it is, not “website website website”.
width and height reserve space before the file arrives, which prevents a jump. A one-megabyte logo displayed at 48 pixels slows the load without adding sharpness the eye can see.
| Hurts | Fine | |
|---|---|---|
| Weight | A megabyte for a small mark | A file the size of the display |
| Dimensions | No width or height | Dimensions reserved in HTML |
| alt | A keyword list | A description of the picture |
| Format | A huge PNG for a photo | A compressed file that fits the image type |