secure image upload

in my website i have a image upload options for users to upload their profile image. using that user uploaded a php file into the images folder. i am a programmer myself and i need help. bidder must have more experience in php and hacking techniques. i wanted to know how they uploaded the php file bcoz i am the one who coded the script and i thought it is enough to protect but it is not now. I have attached the part of the code. check the file and PM me your thought what went wrong and how they did. your part of work it to find the fault and make it stronger. i want it to be done asap