For "typ_skanu" (assuming you mean the select value), you should be using $_POST["typ_skanu"].
Only type="file" inputs would be in the $_FILES array. And yes, "tmp_name" is a standard $_FILES key for file inputs. Take a look at the PHP manual (about a quarter down the page) for more info on $_FILES.
To replace how you currently read the file:
$hndl=fopen($_REQUEST["skan"],"r");
$isize=sizeof($_REQUEST["skan"]);
$imgdata="";
while(!feof($hndl)){
$imgdata.=fread($hndl,$isize);
};
$imgdata=addslashes($imgdata);
You could just use:
$imgdata = file_get_contents($_FILES["skan"]["tmp_name"]);
$imgdata = mysql_real_escape_string($imgdata);