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 MLA Handbook indicates that images (illustrations and tables) should be placed as close to the text they relate to as possible (4.5). Each image should include a caption directly below it which will include the citation information. If the caption provides the full citation and if the source is not used in the text, then no entry is needed for the image in the Works Cited list.
A few notes:
Ideal situation - have all information. Image is found on the web.:
[[Image]]
Fig. 1. Artist’s last name, First name. Title of artwork (italics if it is a work of art). Year. Name of institution/private collection housing artwork. Title of database or website. Publisher/sponsor of database or website. Medium consulted. Date of access.<URL>.
OR
[[Image]]
Fig. 1. Artist's last name, First name. Title of the artwork.
Works Cited page (remember the hanging indent):
Artist’s last name, First name. Title of artwork. Year. Name of institution/private collection housing artwork. Title of database or website. Publisher/sponsor of database or website. Medium consulted. Date of access.<URL>.
BARE MINIMUM example:
Fig. 2. Title of image or your own description of the image. Title of the website where it was published (not Google!). Publisher. Date it was published (if you know it). Web (medium). Date that YOU saw it (today's date). Abbreviated URL.
This can be a lot of information to put under the image. Another option is to use a shortened citation and include the full citation in the Works Cited list.
Fig. 1. Machol, Dan. "Turtle." Flicker, 30 July 2007, <URL>. Accessed 13 May 2015.
OR
FIg. 1. Machol, Dan. "Turtle." (complete citation will be in the Works Cited page)