in your script, just validate to make sure the file extensions arent in your banned file extension list. you could do this with an explode:
$temp=explode(".",$input)
if(($temp[$last_element]!=str_to_lower("jpg"))&&($temp[$last_element]!=str_to_lower("gif"))&&($temp[$last_element]!=str_to_lower("jzip"))){
echo "failed";exit;
}