By mistake I have deleted very important photographs from trash bin of my
Gmail nearly 40 days back. Can anybody kindly help to get it back.

Highly unlikely that you will be able to get these back, especially after the time that's passed.

The only thing I can think of is to either check your computer under "downloads" and see if they are there, or in your "temporary files" somewhere (provided you have not cleared your cache or rebooted recently) or ask whoever sent you the photos in the email in the first place if they could re-send them to you? However, if you have not deleted/emptied your trash, I found this info: http://mail.google.com/support/bin/answer.py?answer=78353