One of the biggest issues when photographing art is getting rid of the lens distortions.This barrel morphing of the edges and keystoning, (that trapezoidal effect you see when a projector is at a slant to the screen) means that the frames will not align with the edges. There are some steps you can take when you are taking the photo, like using a prime lens , rather than a wide angle, or especially a wide angle zoom and photographing the work straight on and avoiding strong direct light.
Perspective correction in Photoshop can be used to fix these effect, albeit with a bit of a learning curve. The new upright feature in Lightroom 5 beta is a very easy to use alternative, and ideal for “Fine Tune” straightening up the edges. The above snaps where taken of my art works hanging in private homes, taken hand held in place they hung on the wall, so I was not always able to take a distortion free set up.In Lightroom 5b before I do any other editing I go down to the Lens Correction/Basic Tab and then use either the Auto (which tries to fix the main distorts or the Full (which I probably prefer) which attempts to align both vertical and horizontal strong lines, like the picture frame. I then crop to the art work and do any other exposure adjustments. Remember it is important to get the white balance right but avoid over post processing so you keep the colours real, It’s that easy!