Hi-
I'm not entirely sure what you're up to, but showing a still image for as long as you want is the easiest thing in the world, using
AviSynth. I get the feeling you want to join it with a video or do something else with it in relation to the video, but neither the title nor the post is entirely clear about exactly what. Anyway, as an example, End=150 frames, the FPS is 30, so it shows for 5 seconds:
You can put the picture on top of the video on any part of the video, beginning and ending whereever you like. It's all basic
AviSynth stuff.