Ask the Library: Reference

APA doesn't require a full citation for photos; what they ask for is a caption (sections 2.12 and 5.23 of the APA manual): "Include within the caption any acknowledgment that a figure is reproduced from another source." (p. 160)

You should always ask for permission and then state in the caption something along the lines of: "used with permission from..." 

You could also use images from the public domain or that have been labeled for reuse. You can look for public domain and  images marked for reuse to use through Flickr, Google, Unsplash, Creative Commons, Wikimedia and many other sites.  For example, with Google images you can click on Tools > Usage Rights > and Labeled for Reuse.

Also avoid using images of products... They may not want to be associated with your research poster.