I have taken a bunch of photos with my phone of a slide presentation, but I took them sitting at an angle from where the projector was. How can edit the images so that they are re-centered with respect to the content of the presentation in the image? Preferably in an scripted manner, since I have a whole bunch of them. EDIT: I initially would just want to correct the skew in an automated fashion.
The feature you are looking for will be called perspective correction in most graphics apps. There is a perspective correction plugin for the Gimp. Here is a tutorial on performing batch operations in Gimp. There is also a tutorial on performing perspective correction using Panotools.