Batch Picture Resizer basically does just what its name says, resize your images. Myself, I prefer Xnview [xnview[.]com] for this sort of thing, because 1) I can use a portable version across more than one copy of Windows, without installing in each, & 2) it gives me the choice of *How* I want the resize performed. You see, no matter what you do resizing an image, going up or down, it means some amount of quality loss, period -- unavoidable. So they've developed several methods of resizing, and which works best depends on the circumstance and often the speed at which you need the resize performed.
help.corel[.]com/paintshop-pro/v20/main/en/documentation/index.html#page/Corel_PaintShop_Pro/Resizing_images.html
wikipedia[.]org/wiki/Image_scaling
Batch Picture Resizer, perhaps unusually, uses a couple of video apps, ffmpeg [ffmpeg[.]org] & mp4box [videohelp[.]com/software/MP4Box], & ffmpeg itself provides several methods for resizing -- ffmpeg[.]org/ffmpeg-scaler.html. Only catch I see is that Batch Picture Resizer doesn't let me choose [as far as I can tell]. It also does some lossless jpeg rotate & flip stuff, same as Xnview, but because of the way that jpeg works, rotate is going to often result in a column or row [or 2 or 3] of lost pixels. Ideally you should be given the say so on how that's handled.
Batch Picture Resizer itself just adds the programs folder, & 200 or so new registry entries. It includes the registry entries to add it to the Windows shell menu, whether you choose the option to add the app to the right-click context menu during install, or not, which is why you'll be asked to restart Windows if you remove the app.
At any rate, nothing wrong with the app really that I can see, and the developer has been both loyal & generous to GOTD over the years.