Captcha before uploading a shot

Why is it there? Why do you need to type in these strange words before you can upload a shot? Probably even more annoying is finding out that (after finally being able to match the 'words') there are no free slots of the movie you want to upload a shot of. I usually end of typing in those words for a dozen movies before I find a movie for which there is a free slot. It would be better if you could see if there is a free slot for a movie before typing in these annoying words...