You should provide sources for images you use in a paper, presentation, or other venue, just as you would cite authors of works that you have quoted. This means that you need to provide specific information about the site where you found the image.
Many people simply cite "Google Images" for images they have found using a Google search, but remember that Google isn't the real source of the images - it's the site that did the searching! If you were quoting from an article on a website you found through a Google Search, would you cite Google for that? Of course not - you'd cite the article and the website where you found it! Images are pretty much the same: you want to provide the specific address of the website on which it was located, not the Google results page.
In-Text Citations and Captions
Check with your professor to see if they have any specific preferences for your in-text citations. Generally, you should label each image with "Figure" or "Fig." followed by a number, and then provide as much of the following information as possible. When you discuss the image in the text of your paper, write "(see Fig. 1)" when you refer to the work.