I haven’t tried this myself yet, but someone suggested what I think is a cool idea:
Do as Jerry suggests, blow up the image by 133% and put it behind the 4:3 version,
so the viewer sees the unstretched full image but with a compatible background on the sides. You
might have to play with the background image (blur, saturation, etc.) to make it work
best.
The best thing though is, scan the images at high enough resolution so you won’t
lose any res when you put them in the 16:9 timeline. I do a lot of stills with pans, pulls,
and pushes, and generally there’s plenty of extraneous image area top and bottom.
Ed