Anna Faris posted a photo she thought was innocent enough, but people on social media almost instantly began an attack over her weight ... and the onslaught was so brutal she deleted the pic.

Anna posted the photo with the caption, "Having pre-show jitters- so glad Michael Sherman captured it- also I eventually decided to put on pants." Michael Sherman is her assistant for her podcast, "Unqualified."

People on social media pounced, saying things like ... "You look so unhealthy, eat." Another says, "This is alarming!" And yet another says, "I feel this pic is a cry for help, I hope you get the help you need."

There are people who are embracing Anna, one saying, "You are beautiful at any size. Health is our concern. If you're healthy and happy that's all that matters! Continue to be awesome!"