How to cite software used to produce data/images?
Some software may have citation requests in their web-pages. The following are a few examples


Matplotlib: Hunter, John D. "Matplotlib: A 2D graphics environment." Computing In Science &amp; Engineering 9.3 (2007): 90-95.
MATLAB: MATLAB &lt;version&gt; and &lt;toolbox&gt;, The MathWorks, Inc., Natick, Massachusetts, United States (&lt;year&gt;).
Origin: Origin (OriginLab, Northampton, MA)


Otherwise, you may adopt the following format:


  Software [version], Company, Year, Link, Last visited: Date.


Also bear it mind that you may not need to cite the software used for image production unless the software itself produces some data used for scientific inference in your work (as mentioned by @DSVA's comments).