[PHP] File Uploading Security - Urgent please

[Statbat]

Hello,

I am doing file uploading of only jpg file format, It first copys in tmp directory 
then I copy it in main.... well you all know the procedure... neways what I am 
concerned is how can I check that the file in temp is correct file and is safe for me 
to copy it in the main folder?

Regards
Statbat