This program tries to find every image in selected folders (and subfolders) and to compress it without losing any quality by using Magic.NET. Usually you can get around 10%-20% compression this way for photos.
If something will go wrong your files will be left unchanged.
Also it completely ignores everything in system folders like "Windows", "Program Files", "ProgramData" and "AppData". But I still suggest you to don't pick folders that contain some programs within.