To avoid using someone else's copyright protected images you aren't allowed to use for commercial or even personal use, Google Advanced Image Search has got you covered.
If any file can not be deleted, then you can use the program LockHunter, which removes the active connections of other applications to that file, which allow you to change or delete file.
Neat little trick to force the preview images of running programs in Windows 7 taskbar or a so called Aero Peek, to show instantly with no delay at all.
To ensure the authenticity of a document you have to sign the document with the certificate. I will show you how you can easily sign PDF document with the help of simple tool DigiSigner.