Charlie Sheen/Brooke Mueller's Son Bob -- Photos Allegedly Show Son Injured During Visit with Mom

TMZ obtained these pics from sources connected with the L.A. County Dept. of Children and Family Services ... and they purportedly show 4-year-old Bob Sheen before and after a visit with Brooke Mueller ... we've learned Charlie Sheen believes it's proof she's NOT a fit parent.

DCFS sources tell TMZ, Denise Richards -- who has temporary guardianship of twins Bob and Max -- included the before/after shots in her letter to DCFS, claiming a photo was taken just before Bob was dropped off at Brooke's place on July 26 ... and the other taken after leaving Brooke's care.

Denise didn't say what the red mark was, but we're told Charlie believes it was a burn.

It appears Brooke told DCFS Bob's face was already red when Denise dropped him off.

As we reported, according to our DCFS sources ... Denise recently wrote the letter to DCFS in order to say she could no longer care for Charlie and Brooke's twins because they have become out of control and violent, hurting her animals and her daughters.