Simply, images are created by someone. Whether a person took a photograph, painted a piece of art, or created a digital image does not matter. If it was not created by you then give credit to the person who did create it.
You also have to check to see if the creator has given you permission to use the work. Please make sure you review the Copyright considerations when using images.
When you find the image you want to use, make sure you keep the following information so you can make the citation::
The 6th edition of the Publication Manual indicates that tables and figures should only be used when necessary to display information concisely. A figure is defined as "a chart, a graph, a photograph, a drawing, or any other illustration or nontextual depiction" (American Psychological Association, 2012, p. 125). It is important to remember that tables and figures are intended to supplement the text so, as rule of thumb, if you are not planning on referring to the table or figure in your text it is not necessary so do not include it. Ideally, your table or figure should be as close as possible to the text discussing it. However, some teachers prefer to have tables and figures in the Appendix. Remember to check and follow or teacher's requirements.
In the body of your text refer to the table or figure by its number. Do not refer to where it is located because that could change (ie. 'the table above" or the figure on page 2). Instead: ..as shown in Figure 1, the animal cell...
A few notes:
Ideal situation - have all information. Image is found on the web.:
Figure X. Descriptive caption of image. From Image title or title of webpage, by Creator’s Name, Year of creation, Database/URL.
Figure 1. Animal cell. Description. From "Title" by A.A. Author, 2015, Appropriate website not Google Images.(you do not need to include the URL if you are including the full citation in your Reference page)
Figure 1. Animal cell. Data from or Adapted from ...
Reference list (remember the hanging indent):
Generally, you would not include tables and figures in the Reference page separately. Remember, you should have referred to the material within your essay so you will have already included the source.
Creator's last name, first initial. (Role of creator). (Year of creation). Title of image or description of image. [Type of work]. Retrieved from URL/database