Straighten an image
This is a very simple trick and it works in every version of
Photoshop.
1.
Scan or open your image
2.
Select the "Measure Tool"
(in the group as the "eyedropper") and draw a line
on what "should be" straight on your image... edge,
horizon, table, wall... anything goes!
3.
Select >Image>Rotate>Arbitrary... and
just like magic, Photoshop has filled in the "angle"
field...