snap to grid Photofiltre 6.5.3

[Shinnen]

Hi,
I'm trying to make rectangular, a picture that is not quite rectangular, and has slightly curved edges (like one would get from taking a picture of a picture on one's wall, at an angle). I was thinking that a combination of the polygon tool and 'snap to grid' might do it, but my snap to grid doesn't seem to do anything. (I admit I don't really know what it's supposed to do anyway.). I appreciate any help.
Thanks,
...... john

[Antonio]

but my snap to grid doesn't seem to do anything
==> it is only to create or move a selection. To understand try to create and move a rectangular selection with this option

[Shinnen]

Hi Antonio,
So 'snap to' is not intended to force a non rectangular section to a rectangular shape?
..... john

[Antonio]

no

[Shinnen]

Good...... thank.
..... john