Musical iconography is concerned with the depiction of music in the visual arts. It is a discipline in its own right, covering the illustration of musicians, instruments, music-making, and the use of musical imagery.
A digital library of nearly one million images in the areas of art, architecture, the humanities, and social sciences for research and pedagogical purposes.
https://images.google.com/
Purports to be "the most comprehensive image search on the web."
https://mimo-international.com/MIMO/
A database of information about musical instruments held in public collections, containing more than 76,000 images.
https://db.ridim.org/
The RId'IM database contains images and descriptions depicting music-making, musical instruments, and similar related objects. Where possible, there are links to online images of the artwork.