Creators of images have rights, such as the right to say how their image can be used. That means that you need to look carefully at the permissions the creator has granted. Make sure you are not violating the permitted use given by the creator.
The following websites provide collections of images you might be able to use. In many cases, the creator's permissions are next to the image.
1. Did the creator grant you permission to use their work?
This can be challenging to determine, so err on the safe side and look for images with a Creative Commons License. Examine the permissions in the license. Look at the different licenses here:
"The Licenses" by Julie Kent is licensed under CC-BY-NC.
2. What information do I need to provide near the image (or at the bottom of the page)?
"A good rule of thumb is to use the acronym TASL, which stands for Title, Author, Source, License.
Title - What is the name of the material?
Author - Who owns the material?
Source - Where can I find it?
License - How can I use it?