Lindsay Lohan was at a house party last week POUNDING TEQUILA ... at least that's the way the guy who handed Lindsay the bottle wanted it to appear when he set her up for this photo.
Sources close to Lindsay tell us .. the actress was hanging out in Venice last week when a friend-of-a-friend asked if he could take a picture with LiLo.
When she said, "yes" -- we're told the guy handed her the bottle and told her to smile! Lindsay is telling friends she didn't take ONE single sip of alcohol that night and put the bottle back down after the photo.
Here's the thing -- it's TOTALLY legal for Lindsay to drink ... but still, we gotta ask ...