There are many excellent online resources for still images, some to which the University subscribes and others which are openly accessible online. The University of Birmingham also has an incredibly rich variety of cultural assets and collections on campus, some of which are digitized and may be accessed, with permission, by approaching the relevant institution.
Remember wherever you source your image you must always use a sufficient acknowledgement this should include the artist/author, the title of the work and the image source. See the Copyright and Referencing your images tabs for more details.
The University of Birmingham subscribes to the following image collections:
TinEye - Reverse Image Search
If you have an image, but you are not sure what it is try TinEye , a reverse image search engine which allows you to upload an image and then searches the internet for other instances of that image.