[Gimp-user] Unskewing images of flat rectangular objects in Gimp

[Elmer Wix <elmer cabekaziruronometu wix gmail com>]

I often use my digital camera to take pictures of flat, rectangular
objects, like framed paintings on a wall, book or album covers, or
pages of documents.  Of course, I can't take these pictures straight
on and perfectly level, but that's OK.  I know what the dimensions of
the objects are, so I can just correct the perspective in software.

In Graphic Converter (a Mac OS X app), I just use the "Unskew"
function.  I simply need to select the four corners of the rectangular
object I photographed.  (Guide lines connecting the four points helps
me to locate them.)  After I've located the four corners, I tell it to
"unskew" and a rectangular image is produced.

Does Gimp have any function like this?  I found the perspective tool,
but that requires me to manually shift the perspective and eyeball
when I think a rectangular image is produced.  That's not nearly as
convenient.