To cite an infographic, follow the MLA format template.  If the infographic does not have an official title, provide a description of it. If you link directly to a PDF of the infographic, it is usually sufficient to cite the PDF as a standalone work and not one contained by the website hosting the link:

Infographic. Johns Hopkins Center for a Livable Future, www.foodspanlearning.org/_pdf/lesson-plan/JohnHopkins_info_0714.pdf.

If the infographic is embedded in another work, such as a blog post, one option is to refer to the infographic in your text and create a works-cited-list entry for the work in which the infographic is included:

The 100 Most Popular Keywords on Google infographic shows that the term most searched for during the twelve-month period ending 1 June 2018 was weather (Brumberg). 

Work Cited

Brumberg, Robby. “Infographic: Google’s Top 100 Keywords.” Ragan’s PR Daily, 19 July 2018, www.prdaily.com/Main/Articles/
Infographic_Googles_top_100_keywords_24740.aspx.

Another option would be to treat the infographic as a work contained in another work:

100 Most Popular Keywords on Google. “Infographic: Google’s Top 100 Keywords,” by Robby Brumberg, 19 July 2018. Ragan’s PR Daily, www.prdaily.com/Main/Articles/Infographic_Googles_top_100_keywords_24740.aspx.