Often you can identify a work of art by reverse image searching - uploading a picture of the artwork you have and searching for matches.
Many museums have started making high quality images downloadable without permissions (for art objects in the public domain). The following museums have made at least some of their images available for free re-use. You can explore a database of museums with Open Access image policies at the OpenGLAM website
Some museums restrict access to high quality images, and only allow smaller images to be downloaded. To get the high quality images you may need to request permissions and sometimes pay a fee.