Robin Williams' Last Photos Before Suicide

These are the last known pictures of Robin Williams ... a day or so before he committed suicide.

A frail Williams was at an art gallery reception Saturday night ... near his Bay Area home. He surprised local artist Mark Jaeger -- a ceramics teacher at Marin Catholic High School -- whose works were featured.

Jaeger tells TMZ Robin was there for about an hour, seemed in good spirits ... laughing frequently. Jaeger says Williams was not drinking.

Jaeger's art includes a "superhero sculpture series" ... Robin purchased one of his superhero clay heads in the past. The artist says he and Williams were talking about a possible script based on the concept of his sculptures ... a homeless superhero who comes out during the night to help people in need.

Robin was there with wife Susan Schneider ... the woman in the foreground with dark hair. We're told Robin spoke to Jaeger's students and seemed engaged.

The pic was taken at 5:45 PM Saturday. Robin's body was discovered Monday morning.