You have to distract the gaurd.
You need the picture from you room.
First tap on the roots to the left of the guard.
Sneak behind the pillar.
Wait till the guard goes back. You are still behind the pillar.
Put the picture in the dark area. Now put the lighting bug above the picture.
Now when you distract the guard he goes over there to look at the picture.
Here is an old video walkthrough I found for the steam version.