I think he's at number 12 Grimwald Place cleaning up his godfather Sirius' things.

im thinking its his detention with snape reading his fathers and serius and lupins misdeeds

he's on a panty raid. duh.

Ok, this is what scene i think this pic is from. I believe its when Harry takes Ron to get the anitdote from the chocolate cauldrons spiked with love potion. Slugghorn cures Ron and they celebrate by sharing the mead thats spiked with poison and Harry runs to the cabinet to get the bezor to shove down Rons throat. Since Rons birthday day was on a saturday that would explain the muggle clothing. Any thoughts?

personally i dont think it is detention. it doesnt seem "dark" enough in the back drop. he doesnt look frantic enought for it to be the scene when hes hiding the book or getting the bezoar for ron. but it looks like slughorns office (or what i image slughorns office to be like) so i think it is something not in the book but something to fix one of the problems that the people making the movies messed up earlier.

I think it's Harry getting his HBP book out of Slughorn's drawers in his first potions lesson. The trunk has an S on it so it could be Slughorn's.

i thnk he is looking for felix felicis in his school trunk,the lucky potion which he won in his first class of potions from slughorn