XnConvert 4+

Program works well and is great for batch processing, but with a catch if you are running Catalina. The app hasn't been updated, so it doesn't know to ask for permission for writing to the disk. This means all the conversion fails with a 'not to useful' error of "create error". The work around is to manually grant it full disk access in SystemPrefs/Security&Privacy -> Full Disk Acces (Left pane). (Unlock panel before making change) by clicking on and selecting the app from the Application folder.

I had a bunch of images I was using for wallpaper, but some of them were intended for vertical use and I was not using my monitors vertically, so these images - several of which I liked - kept making my desktop look strange. In a folder of nearly 8000 images, finding the vertical format ones and removing them would be a serious pain, as would opening Photoshop and rotating them. This app let me drop the entire folder in and process in one go, rotating just the portrait formatted images, and even let me append the new resolution to the end of the filenames. Five minutes of work and another ten of processing gave me a perfect set. There's a ton of other convenient options, too, which will be very useful in the future; this is a very powerful app! But you've wasted all this time reading, stop now and just download it already.

There are so many options available in this utility, and the best part is that it’s all free!

The workflow provided for converting and editing files in batches is incredibly powerful. I’d argue that the only way you’re going to get more options than this is to do it from the command line, and even then this program just makes it so much faster and easier to do.

I would have paid for this program if it wasn’t free, that’s how good it is.