Each writing style has specific instructions regarding how to cite images. Check the handbook for each style for info. Remember that artwork is also information and a creative product, so "authorship" needs to be noted when you use someone else's work.
Even if an image has a Creative Commons license that allows you to use it, make sure you read the details of the license and follow those directions.
When conducting research, the same rules apply to images in terms of plagiarism and copyright. Always be aware of where you found your image (or text). Cite it and/or attribute it.
Questions to Ask Yourself:
Make sure you choose 'Creative Commons licenses'. Read the license and follow the directions. You will still need to cite your image, following your manual style (Chicago, APA), but you might also need to attribute the image. Citing and attributing can be two different practices.