Well it depends on what you are going to do with those posters. If you're just going to make up some posters and hang them up in your own place, who's going to find out? If you used a still from let's say a J'en ai marre performance, the rights to those videos and any stills that may be captured of those videos, belong to someone else. I'm not sure if it's Polydor or Universal or MF/LB or whoever who owns those rights now, but they are not going to be pleased, seeing other people making money off of something they own the rights to. There are also some very good stills taken during En Concert, but the rights to those too belong to someone.
A few years back, I saw 3 posters of the same picture of Alizee for sale from some place in France. I bought them and sold 2 to other people I know and I thought of having copies made of the one I had and offering them 'privately' to other fans. This was a promotional poster and I believe it has copyright labels on it, meaning you can't legally do what I wanted to do, but this was several years after the height of her popularity peak and these weren't being printed any more so it wasn't really costing the owners of the rights to the poster anything if a few people here and there had some posters made. I had found someone who I think would've copied it, but at some point the idea fell by the wayside.
In this thread, you see the name Karen in several posts. She was a member who made several covers of cds and albums and she put together some good videos too. She seemed to suddenly disappear at one point and I'm not sure if it's true but I heard it's because those covers went a little too far.
Alizee forum was one of the bigger fans sites out there. They got into trouble because they started posting ads which meant they were making money off of Alizee and they were almost shut down because of it. So you have to be careful about what you do and how you do it.
Alizée_-_En_Concert_-_poster.jpg