I use Irfanview for images on a PC. It's pretty basic and easy to use, and I believe it has the ability to stitch JPEG files together. It's a free download.
https://www.irfanview.com
There's another free downloadable photo editing software called Gimp. I've used it a little and it seems easy enough to work with. I haven't tried stitching photos together with it, but I think it has the capability.
https://www.gimp.org
Another thought is importing the individual JPEG files into a PDF document and stitching them together there. Again, I don't have experience but someone else may be able to help.