It really depends. There are lots of factors. First: size/style. You have to figure out if they are one sheets, half sheets, inserts, etc; whether its advance, style A, B, etc. Then there is condition, restoration that has been done, etc. Also, for certain movies, like Casablanca, you have to figure out which release it's from. Casablanca has been released dozens of times, from its original release in 1942 to its most recent 70th Anniversary release a few months ago. Posters from the 42 and other 40s releases are most collectible, thus most valuable. Prices range dramatically based upon these and many other variables. For example, original one sheets for the original release of Casablanca in 1942 go way upwards of $4,000. They are unbelievably rare. There are none on eBay, and the only one listed on CineMasterpieces is for $35,500. (They are a bit pricey in my opinion; the same poster (though slightly worse condition) recently sold at Heritage Auctions for $28,680.) At the other end of the spectrum, posters from the 61 or 74 or more recent rereleases go for a couple hundred dollars or less. The only one I've seen that looks like the one you have is a 1960s Belgian release. If it measures 14" x 22" and has non-English text (besides names, logos, etc) then that's probably what you have. One recently sold on ha.com for $418.25. Your best bet is to take it to a local dealer who can measure it and inspect it closely. If your looking for online resources, check out cinemasterpieces.com, movieposter.ha.com, or filmposters.com, but like I said, try to find a local dealer if you want accurate assessments. Jumping into the movie poster collecting hobby takes time and learning. One resource for education (not prices) is learnaboutmovieposters.com. Check it out.