How to delete selfie pic as background on message screen?

[AC Question]

A selfie of me appears on the message screen as Background on every text message received or sent. How do I remove this selfie? I think that I may have mistakenly added the selfie pic as Background using the CM Security app, but there are no options for deleting it.

 

[B. Diddy]

Welcome to Android Central! Which phone, and which messaging app?