Welcome to the Q&A Forum

If you have permission to use their images, just get images from them, name them accurately, and give them accurate alt-text. Duplicate content has to do with your own content, in general. Since the point of naming images and alt-text is to help Google understand them, it's not a big issue if an image has the same alt-text as another or appears multiple times on the site (especially since they should all be coming from an images directory, no matter where they are on the website). Also, images are much more likely to be naturally reused than text, as licensing photos is a long accepted practice.

Irving, thanks once again for your thoughtful response.