There are many image databases and image collections available on the Internet, via museum, archive, gallery, library and research websites.
Some examples include:
Art UK - the online home for art from every public collection in the United Kingdom
Collage, the London Picture Archive- contains over 250,000 images of London from the collections of the London Metropolitan Archives and Guildhall Art Gallery
The Met's Collection - 375,000 images of public-domain works are available under a Creative Commons Zero (CC0) to use, share, and remix - without restriction.
Images can be searched for using keywords or tags. The following are just a few examples of sites to get you started:
Conducting a successful image search can depend on terminology, related terms, and alternative spellings. For example ‘war’ might also be ‘conflict, combat, warfare’. For more information about searching techniques, please see our Guide to Searching Techniques.
Context based image retrival is a means of searching using critiera such as colour, shape, texture or even by uploading your own image and using that to search for other images. Examples of websites that allow this method of searching include:
Google Images - Allows you to search by uploading an image
Tineye labs - Search by colour or image
Panoramio - Search by location
Online and print journals are another source of images.