Editing wasn't used to be as it is today. Back in the day editing of images wasn't done with the help of computers. So before computers and the mainstream image editing software were invented, people used to edit images with their hands. Most of the editing in earlier days was done through manipulating the negatives of the photos. 

Earlier this method was used by a lot of people to add ghosts silhouettes to photos of soldiers who died in battle. One of the most popular examples of this practice is an image of the spirit of Abraham Lincoln behind Mary. This image was made by William H. Mumler.

Fast Forwarding to the 1980s, Adobe launched its first Digital Photo Editing Software, which was nothing short of a revolution for the image editing industry. Not only the software, but Adobe also announced many other tools and other product lines that eventually made it much easier for Photographers and Editors to edit their images. 

And skipping today, we can easily see hundreds of Photo Editing Tools that are free as well as paid. But among all the photo editing software developers, Adobe has always managed to stay at the top no matter what.