- I'm not a lawyer and this is not legal advice -
For any images where you are not the creator:
For images where YOU are the creator:
Google Images is a powerful way to search for images, especially using the advanced search by clicking on Tools. You can search for a specific size, type (eg line drawing) and usage rights. Example below. The usage rights are listed here by Google in order of reusable in most circumstances to least reusable. Often once you get to the image, it may have a Creative Commons license, CC-BY and CC-BY-NC being the most common. In those two cases, the creator is telling you that you are free to use the image with attribution. NC equals non-commercial use.
The following websites detail various citing situations with images (e.g. tables, figures, graphs).
Citing tables, figures and images: APA (6th ed.) citation guide, by Simon Fraser University Library.
Citing and referencing: Figures and Tables, Monash University Library.
Example of labeling a figure within a paper:
Where did that image come from? Don't lose track!
Decide on a file naming system that makes sense to you eg krebs_pyruvate_detail_ccby.png
You can drag the image to a location in your Zotero library, and enter any necessary citation information (look for a box that says "rights" or "extra" to add information you'll need later to keep track).