Start by considering
Who might have collected images relevant to your topic? Perhaps an institution, organization, profession, or expert has worked to gather images that could aid your research. Do they provide access to their collections?
Where might relevant images have been published or distributed? This could be an interdisciplinary or subject-specific database, online image repository, professional group's website, or more! There are many places to look. Where might you expect to find them?
Has a book, encyclopedia article, exhibition catalog, or dissertation, been published on the topic? If so, check their bibliographies and lists of illustration citations for possible image sources.
Has a research guide been created on the topic? Subject-specific research guides could lead you to more image sources. For example, the Film and Television guide or Gender Studies guide provide more specific image resources pertaining to those topics. Look at the many available research guides on the Browse all Research Guides page.
There are several types of places to search -- databases, online web resources, books/e-books, archives, and more! You may be able to search resources that specialize in your topic or you may need to look at more general interdisciplinary resources. Be sure to search in multiple!