There are freely available image resources.
Some databases allow you to limit (refine) your search so that you only find articles containing certain types of images/drawings.
Avery: Select Advanced Search - Document Features - limit by selecting one or more of the options (illustrations, photos)
ARCH: Select Advanced Search - change in Any field (Show all other fields) to NT - Notes and type in one of: photo*, plan*, secn*, map*, graphic*, plan*, axonview*, elevn*, sketch*, model*, port*, siteplan*, drawing*
A very useful site from Duke University on visual literacy. Includes sections on reading images, research & writing and links to relevant Libguides.