You have numerous options if you need to find an image for your microbiology assignment. Several library databases have visuals you can use, and the advantage of the database sources is that they can assist you with citing the image.
If you do not find what you want in the library databases, you can search for images on any high-quality, credible website. However, you will likely need to construct an image citation. Image citations should include the creator, the date of publication, the title of the image, a description of the image in brackets, and the source (usually the website and URL). Below is an example of an APA citation for an image pulled from a government website.
Elisman, M., & Deerinck, T. (n.d.). E. coli [Photograph]. National Institute of General Medical Sciences, National Institutes of Health, U.S. Department of Health and Human Services. https://images.nigms.nih.gov/pages/DetailPage.aspx?imageid2=6388