Without any doubt the most popular form of photo retouching is resizing images. For this reason a tool like PicResizer is always appreciated.
PicResizer lets you resize hundreds of photos in one go. You just have to drag and drop the photos into the program interface, establish the size (both the width and height) you want, and, automatically, all of them will be resized to that size you chose.
At no moment are the original photos modified, as the new, resized images are saved with a different name.