Most referencing styles have instructions on how to reference figures and other art work.
Cite Them Right has guidance on referencing illustration, figures, tables, etc from other peoples work - change the drop down menu at the left of the Cite Them Right page to see instructions for your referencing style. There is also a Harvard rule for referencing figures and images that you have adapted.
If you want to reference other types of art (painting, photographs, music, etc.), you can find instructions in Cite Them Right. Make sure that you are following the instructions for your referencing style.