Re: Correcting Parallax Perspective (fabrics)
Try to photograph a painting or a drawing so that opposite borders are perfectly parallel and non opposite borders are perfectly perpendicular on your photograph and you'll quickly now what parralax errors mean. To have no parallax error the axis of view of the camera needs to be perfectly perpendicular to the 2D plane you photograph and that's not too easy to achieve as I can recall.
Fortunately it is easy to correct with a computer so you don't need to be overly careful about it unlike in the old times.
The distort selection tool in Photoshop should do. Make a selection. Right click on the selection. Choose free transform. Right click again and choose the distort command. Drag the anchors on the selection to correct what you want to corect. Press the enter key when you are done.
Otherwise a plugin such as Mehdi Projection (free) can also do I think if your photoeditor hasnt't got such tools.
Is this all correct ? Someone correct me if I am wrong.