What you need to know
Alt text is a text alternative for an image, not a caption for every pixel. It helps when an image cannot be seen or loaded, and it lets assistive technology communicate the image's purpose in context.
How to apply it
Describe the information or action the image contributes. For a linked logo, name the destination or brand; for a decorative background, use empty alt text so it is skipped.
Common mistake to avoid
Avoid phrases such as image of unless the image type matters. Do not put keywords into alt text that do not describe the actual image.