Ok, I figured out what was happening with the lingering tmp files and why I was not seeing them. It was only happening if the image did not need resizing, it was a logic error where after creating the tmp file we checked its size and if it did not need resizing we were just exiting the method and this would leave behind the tmp file. I have fixed this both on demo.mojoportal.com and in the preview package.
I've also made it possible to make a cropped image larger than the crop selection, so for example if the crop selection is 100px wide and 100px tall, and you specify 200 for the crop width and height, it now enlarges the crop. Of course quality degrades depending on how much larger the result image is vs the crop selection.
I will see about a way to delete files. I could possibly add a delete button similar to how I'm adding the crop link. I guess my only concern is that users could delete files that they did not upload and files which may be in use in some content that they don't know about. Maybe we need to add a separate permission for roles that can delete files so we can control it separately from who can upload.