For OSM only map images:
Answer legal OSMF.
As per the Attribution Guidelines, “if multiple static images appear on the same document, one instance of attribution is sufficient.” Thus, for a forum like this one devoted to OSM, a website footer message of “map images are from OpenStreetMap unless otherwise noted” is sufficient, without need to label the images individually.
This is a screenshot from the Licence/Attribution Guidelines page.
For not OSM map images:
individual, check licence images.