Does your camera support RAW files? If so, those are usually 12 bit images while JPG is only 8. You throw away most of your data using jpg! JPG supports 256 intensity levels while 12 bit RAW supports 4096, 16 times more! JPG leaves you little room to process the image. Avoid JPG if at all possible until saving a COPY of the image for the net. The image you archive should remain at the full bit depth your camera takes. Also save the original stacked images as you may wish to try again using a different stacking routine. There are three basic ways of combining images for deep sky work (not planetary), Averaging, Adding and some sort of noise rejection routine. If the image contains a lot of information that is already near maximum brightness avoid adding the data unless your addition routine supports more bits than the camera took. If it saves in 16 bit mode and you took the images at 12 then adding is fine. But otherwise use averaging. Both reduce noise equally.

There are several ways of combining that further reduce or eliminate satellites, cosmic ray hits etc. if you take more than about 6 frames. The simplest is median combine. It finds the median value of all images for that pixel in the stack. Thus if a satellite comes through it's track is ignored. The problem is it doesn't reduce random noise as well as the other two so you need more frames. Better is a form of Sigma Reject. There are several freeware programs that handle this though most only support FITS file format that astro CCD cameras use. These programs use a more complicated routine that often reduces noise more than adding and averaging. It's the only way I go any more when I have 6 or more frames to stack.

I've heard Registax supports it, I don't know personally however.

Rick