This forum thread needs a solution.

Strange image on Mac start screen

About a week ago, a new and strange image appeared on my start screen (see round image in uploaded file).  It looks like a detail of a prickly pear.  Wtf??  I have no image like this in my files, and I can't get rid of it.  Right clicking does nothing.  I'm concerned this is/points to malware on my system.  Full scans with Norton, Bitdefender and Malwarebytes all come up clean.

Has anyone else encountered this?  All thoughts welcome.