I made a form which contain, among other things, an input type=file with the name img. Of course, I specified in form tag the correct enctype.
Then, in the action file I wanted to see all my "post" variabiles and I displayed them by traversing the array HTTP_POST_VARS. All of them was there but $img. Although, when I displayed $img using echo I was able to see it correctly.
Has the type "file" of input some kind of special status?