My best guess on the shaky jpgs is that you're seeing interlace flicker. Digital cams, scanners and computer-generated images are square pixel, non-interlaced (frame-based)entities while frame captures from video are rectangular pixel field-based images - two fields combining into one frame/image. When motion occurs in the 60th of a second between fields, it offsets in field two some of the data from field one - along the horizontal. Even de-interlacing such stills can leave other problems depending on how much motion is involved, like a hand waving for example. But deinterlacing is still your best option,even if you have to try some blur as well. I'd also suggest that you not export to jpg for NLE editing work. If you have a choice of export settings as I do in Premiere, select TIF or TGA or even BMP.
David Hurdon
http://www.contentshop.tv