Reg Exp to change c:\dir\dir\pic.jpg to dir/pic.jpg - to upload image path

I am trying to upload images - in fact an image path - from a PC. I use the <input > tag: <INPUT NAME="addpic" TYPE="file"> which nicely gives an input textfield and Browse button! This gives me, in the input box, eg: c:\pics\subdir\pic1.jpg The relative path on the server is something like: subdir/pics1.jpg thus I need to transform the string: c:\subdir\pics\pics1.jpg into: pics/pics1.jpg I can use str_replace() to change "\" into "/". I am looking for an expression from some clever person to get rid of "c:\subdir\" given that I don't know the exact 'subdir' or name of the image. Regards, John