To find reusable images for your posters or presentations, consider four options:
Use images from a site devoted to public domain works, which would allow you to reuse images freely
Use Google Advanced Image Search and select "free to use or share" under "Usage Rights"
Consider images created by the US government (.gov). For example, NIH Image Gallery
Consider images created under Creative Commons or for educational use. For example, Freely Available Images and Multimedia for Educational Use from the Center for Educational Resources, Johns Hopkins University.
MSL has several licensed graphics resources containing images:
Like journal articles, books, reports, web pages, images/graphics also need to be cited properly. You will need to identify the essential elements such as author, date, title, and source. Consult NLM Citing Medicine for rules and examples to cite images.