One of the most difficult tasks in photography is aligning photographs for proper centering and correct geometric perspective. This is true for Second Life. A photography that appears to be correctly aligned at first glance may actually be crooked.
"Straightening" by cropping cannot work if there are strong vertical lines in the subject. The only solution is to align your subject matter correctly to begin with.
The Rule of Thirds
I accomplished this task by uploading a "rule of thirds" texture as a clear PNG file. The rule of thirds is shown above. The rule of thirds allows you to center your images and gain proper perspective, you can read more about this here:
You then construction aone-prim HUD with the texture. The hud should be about .9 meters square, and thin on one dimension. Then attach the HUD to a center position, and you will be able to align your photographs. You can see how much easier it is to align images by looking at the examples on this page. These images were taken at the AZ Emporium Main Store today.