Find an angle that the highlights the defect.
If it's a point and shoot, find the macro setting and turn it on. Then find out if your camera has spot focus. If it does, turn it on (which will focus on whatever is in the middle of the frame). When taking a picture, move the defect to the middle of the viewfinder and half-press the shutter button. If your camera also has manual capabilities, set the aperture (f-number) to the lowest number, which is generally f/2.8 on P&Ss. This will allow you to have the background (in this case whatever the paint is reflecting towards you) more blurred, focusing on the defect.
The reason P&Ss have trouble focusing on tiny scratches is because their autofocus works by analyzing the contrast in a scene. It moves the focus back and forth until it finds the position with the most contrast in the scene, which usually means the reflection of the contrast-heavy scene is what it catches and focuses on, rather than the little scratch.
If it's a DSLR, put your lens on manual focus and figure out just how close your lens will let you get to the defect. Then choose spot focus and the lowest aperture, though with with DSLRs you could stop down the lens a bit more and still get great results. You could keep it on manual focus or put it back on automatic, whichever works for you.
Hope this helps.