Perceivable
WCAG 1.4.5
Images of Text
Don't use images of text — use real text styled with CSS. Images of text can't be resized, reflowed, recolored, or read by screen readers. Exception for logos.
In plain terms
Use real, selectable text rather than a picture of text — pictures blur when zoomed and can't be read aloud or translated.
Why this matters
Text baked into an image can't be enlarged without going blurry, can't be recolored for contrast, and can't be read by screen readers or translated. Logos are the main exception.
How to detect
Quick check
Zoom to 400% — does any text turn fuzzy? Try selecting the text with your cursor; if a block of 'text' can't be selected, it's probably an image. Flag anything that isn't a logo.