One uploaded image, checked against the rules of the marketplace you pick. The automatic re-check after an auto-fix doesn't cost a credit.
What counts as a fix?
One auto-fix run on an image. The before/after view and the download of that fixed image are included.
Do credits roll over?
Yes, up to the plan cap. Cancel any time from the dashboard; unused credits stay usable until the period ends.
Do you store my images?
Checks made without an account are deleted after 24 hours, unless you enter your email to claim the clean file. Images checked or fixed while signed in are stored.