Is this seat post toast?
 

I loaned this bike to a friend after his was stolen. He clearly lowered the seat post and it looks like the binder bolt was over tightened, as you can see the outline of the seat tube and the groove that allows tightening. It’s a carbon post. Can I still trust it or is it too risky?
https://cimg1.ibsrv.net/gimg/bikefor...cb8188b04.jpeg

if there is an indent in the crease, I would not ride it..

Nope it is a seatpost but you probably don't want to ride on it. You have worries and you might not want to ride it. It is hard to really see what is going on as the potential area of concern is out of focus and we cannot touch it and feel the area.

Perhaps the friend would trade you a new seatpost for that one ?

Based on the info given, I probably wouldn’t.

Unfortunately this looks like a case of no good deed going unpunished. Kudos to you for helping a friend, but I'd not want to trust that post and I'd give the whole bike a going over at this point.

yes and your friend should atleast know that carbon needs to be torqued per spec so that he does not damage another, ie need torque wrench.

With a fuzzy picture it's hard to tell but assuming those lines represent a depression in the post, it appears to indeed be toast.