The two most obVIous things which you don’t mention (but you possibly know already) are a) to blur the photos as they are almost certainly way too sharp in relation to your video footage, and b) to add noise or grain, as your video will have plenty and it’s the one thing the eye picks up on immediately if it’s missing. It only needs to be sutble but it just has to be there.
Another trick which probably isn’t right for you here give that you talk about a locked-off shot is to give it a hand held look. By far the nicest and most believable way of achieving this is to take any video camera (your phone will do if necessary) and (hand held) shoot a decent duration of an easily trackable image. Then all you need to do is add that new footage as a layer, motion track it to extract its movement and then link the still to that tracked movement (obviously hiding the refernce video in the process).
Simon Ubsdell
http://www.tokyo-uk.com