I have python 2.7.3 and I want to install PIL 1.7.
I downloaded "PIL-1.1.7.win32-py2.7" and try to install it but it shows me an error messege that it can't find python 2.7 in the registry.

"python version 2.7 requried, which wasn't found in the registry".

I double check and I'm sure that I have python 2.7.3.
what is the problem?

As the message says, PIL installer can't find registry keys, this because python installer put values in 32 bit OS version path "HKEY_LOCAL_MACHINE\SOFTWARE\Python\PythonCore\2.7" but for 64 bit OS version it should be set in "HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Python\PythonCore\2.7".

Easy fix is to copy and paste below in a text file, then change the extension to .reg and run it, it will add the required registry, then install PIL.

Copy from here to the end:

Windows Registry Editor Version 5.00[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Python\PythonCore\2.7][HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Python\PythonCore\2.7\Help][HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Python\PythonCore\2.7\Help\Main Python Documentation]
@="C:\\Python27\\Doc\\python273.chm"[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Python\PythonCore\2.7\InstallPath]
@="C:\\Python27\\"[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Python\PythonCore\2.7\InstallPath\InstallGroup]
@="Python 2.7"[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Python\PythonCore\2.7\Modules][HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Python\PythonCore\2.7\PythonPath]
@="C:\\Python27\\Lib;C:\\Python27\\DLLs;C:\\Python27\\Lib\\lib-tk"