The heading almost says it all but I'll elaborate. Working on a web site for a condo rental in Hawaii required that I optimize some images of the units’ rooms and amenities. The quality of the pics was good but there were problems with keystoning and distortion in most of them. Most Photoshop users are familiar with using 'Edit > Transform' with 'perspective', 'distort' and 'skew' to square up an image but fixing warped images is a less known skill. The best tool for this is called 'Liquify'. You can find it under 'Filter'. This is not a tutorial on how to use the tool but I will note that you can 'freeze' parts of the picture to keep them from being changed while you use the 'bloat' or 'pucker' tools to bend other parts of the image to achieve the desired effect. Setting your brush size large and your pressure light allows you to make subtle changes for the best result. Please let me know if this tip helps you.