If the clip art you are using is from a royalty-free piece of software, the only citation needed is a note of the source's origin after you use the image in your paper. However, if you are discussing the piece of art or want to be thorough in listing all your sources, you can cite the software in your reference list using the following format:
Program Title (Version number) [Format]. Publisher Location: Publisher.
New Millennium Art (Version 3) [Computer Software]. Ithaca, NY: Gorges Intel.
Clip Art Taken From Website
If you are referencing or using a piece of clip art taken from a website, you should include the web address in your reference list using the following format:
Image Author Lastname or Screename, First Initial(s). (Year of image). Title of image [file format]. Retrieved from URL.
Rampa. (2015). Mandala [SVG file]. Retrieved from https://openclipart.org/detail/215148/Mandala_2015_12-by-rampa.