In Plain English
Image SEO combines useful visual context with appropriate alternative text, sensible file sizes, explicit dimensions and suitable formats.
Why it matters
Efficient images can preserve a page’s visual meaning without unnecessary transfer or layout movement. Informative images need an accessible alternative; decorative images normally use an empty alt attribute.
Example
A symptom guide might use alt="Brown, crisp edges on a snake plant leaf" when that visible detail matters to the explanation.
Common misunderstanding
A file name or alt attribute is not a place for a list of keywords, and essential instructions should not exist only inside an image.