Professional photographers use shift lenses (expensive) or special large-format cameras to avoid the undesirable visual effects caused by converging lines in images, especially in architectural and landscape photos. Marcus Hebel's ShiftN is freeware that does much the same thing, analyzing images for parallel lines and correcting the perspective.
ShiftN's simple, efficient interface is divided between two panels, an image pane and an EXIF data view that also serves as a preview pane for image processing. Aside from a file menu bar, this program has five buttons: Open, Automatic Correction, Re-Optimize, Adjust Correction, and Save and Exit. We clicked Open and loaded the program's sample image. We could apply a grid to the image via the View menu. We selected the autocorrect option, and ShiftN processed the image, displaying converging lines and other image elements in the preview pane image. We saved the image and then opened both the original and processed images for comparison. The changes made by ShiftN are subtle but highly effective, shifting the perspective in the frame to a more attractive plane. Next we applied ShiftN to an image of a lighthouse. The correction provided a much more accurate view that didn't distort the width of the structure's base. Using the adjustment sliders, we could drastically alter the perspective to achieve custom effects. ShiftN's Options and Help file make this versatile tool easy to set up, too.
With ShiftN, owners of point-and-shoot cameras can approximate the capabilities that professional photographers spend thousands of dollars to achieve. It's easy enough for amateurs yet advanced enough for pros to use to try out shots before they shoot.
ShiftN permits correction of converging lines a majority of the correction work is taken over automatically by the program. Both the effects of converging lines and poor camera angle are corrected automatically. The process in ShiftN is to search the image first for straight lines and edges, and to consider those which are sufficiently vertical to be likely architectural elements. On the basis of these straight line segments the program runs an optimization process that attempts to determine perspective, correcting the image so the lines are made parallel to each other.
I have used the earlier version [3.6.0] for some years and find it a very useful program for improving perspective. I usually only use it with the automatic correction, but no doubt with a bit of input I could make further adjustments. I would certainly recommend it to others.