While IMAGE MAGICK is a true command line tool, this failed your requirement of some GUI drag and drop. In mainframe days we would write the batch file to do what you asked. So while I think it fit your batch requirement it failed when you added the GUI interface you wanted.
For over 2 years, I have searched for a TRUE BATCH image (picture/JPG) resizer that will process in TRUE Batch and not ONE folder, one screen etc.
Most large picture collections come in SETS, and some have lots of them and they are all different size images depending on the resolution you need. But to store for archive, you need to reduce the size, etc.
In 2 years I have not found any resizer that can handle more than the TOP level folder and NO sub-folders.
Yet most collections come in multi-sets are in multi-folders but all software I have found can only resize ONE picture or ONE folder at a time, which is typically 30-110 pictures and with some having hundreds of sets, meaning thousands of pictures, that is what is called labor intensive doing them a hundred at a time.
Has anyone found a picture resizer software that can handle the top level folder and/or its "sub-folders" and keep them straight? This way if you have thousands of picture, you can load up, leave over night or do something else instead of setting there and waiting for one lousy folder to resize.
Some programmers call their software "batch"; but obviously do not know what "batch" means. It is a old Mainframe word we invented when a computer 'mainframe" could only process one job at a time (PCP) and then multiprocessing was invented and we would 'batch' several programs together. I have been in 'Data processing' about 55 years so i know what batch means. So when I search for a resizer and I find 'batch', the instructions say to 'drag and drop' one picture or one folder, or one screen??