I you are scanning them then use a lossless format like BMP or TIFF. Just remember that the actual video frame is only 720 x 480 pixels (720 x 576 for PAL) so it won't matter that much. I think a low compression JPEG will give exactly the same result and the file will be much more managable.
If you already have the pics just use whatever format they are already in. There is no point losing a generation by converting them to a lossy format and converting them to a lossless format will only increase the file size, not the quality.
If I was scanning them I'd probably do TIFFs in 720x480, any bigger is unnecessary.