Deform an image to correct perspective

Import the image (File > Import > Canvas Image) or pick the layer to be adjusted in the paint layer editor.
Choose Paint Edit > Deform Image Layer. The active image layer will display manipulator handles as shown below.

Current settings of this tool:
Pick and move the right top corner handle using the . (Action = Unconstrained corner deformation)
Select and move the center right handle with the to make the image wider. (Action = Unconstrained edge deformation)
Select and move the left top corner handle with the . (Action = Unconstrained corner deformation)
Select and move the right corner handle with the to make the image wider following the 2 point perspective guide lines. (Action = Constrained corner deformation)
By using the vertical & horizontal bias controls in the option window you can deform the center of the image, that is, pull or push the center of the image towards or away from the perspective point.