I have LG KU900 and by mistake I delete all my photos. How can I get them back?

First thing to note is that the deleted data on the phone will remain there until something new is saved and overwrites it. This might not happen immediately but eventually, after continued use, it will.
Either connect the phone straight to a PC using a USB cable (if supplied with the phone) or take the card out and put it in a card reader attached to the PC. You should see memory card shown as a drive letter (like H:) in Windows Explorer.

Then try some photo recovery software on the PC. This should recognise the phone or card and then you can scan it using the free download of some good photo recovery software. That will show you what files still exist on the phone or card and what can be recovered.
http://download.cnet.com/Asoftech-Photo-Recovery/3000-2094_4-10913438.html?part=dl-10913438&subj=dl&tag=button

Use recuva. its quick, free and works well for files deleted from the trash can

Don't be so worried about ur pictures. There are some gud photo recovery software available on internet. But first of all please stop using d card anymore to increase d chances of recovering files. Then you need rely on professional photo recovery tool. Download any one of the software from the following sites
http://www.photo-recovery.net/ or http://www.digitalcamerarecovery.net/ both are gud ones

Connect your phone to a computer using its PS Suite so you can manage its phone and memory. then from your computer you must download a recovery file to recover all files you deleted. follow this link: http://www.raymond.cc/blog/archives/2008/01/24/top-10-free-data-recovery-software/