A credit line gives information which describes the work itself and is placed near the artwork. A citation is used to give enough information to readers so they can find the exact resource you used and are referring to.
A credit line for an image includes: Artist’s Name, Title of Work in Italics, Year, Medium/technique, dimensions (H x W x D), Image Source with shortened direct hyperlink to the image. The credit line should be placed right next to or below the image. Here is an example:
Andy Warhol, Marilyn, 1967, screenprint, 36 x 36" (91.5 x 91.5 cm), MoMA