So I have the video strip but now I want to add an image on it, like I would add a text.
You can also use standard blender text (and other objects too) superimposed to your video, like in the below example, where I higlighted important settings:
The blender object(s) are in the "scene" strip, and since the scene has transparent background, it can be superimposed to the underlying video strip, using a standard alphaover effect.
I just noticed the background video is horrible and has hiccups, but that's just the first video I found on my disk... it's crappy by itself... don't mind about that.
Make sure that the text image has an alpha channel to show the video strip below on the timeline. Also make sure that the new image strip has its properties (n-key) set to Blend type: Alpha Over.