Photos get wrong orientation on iPad 2

I have an iPad 2 with iOS 5 and a Windows XP PC. There are about 2300 photos on my computer and their orientation (landscape, portrait) are correct. When I transfer them to my iPad using iTunes, some of them show wrong orientation in Photos on my iPad. I change orientation on Windows and sync again, but no effect. How can I fix the issue?If you have the same problem, try the following methods:*