I accidentally deleted all my picures from my memory card. How can I retrieve these photos?

You can retrieve those photos & if you want to maximize chances of memory card files recovery, the first thing you should do is immediately stop taking more photos or videos (with your current camera memory card) in case partial files are overwritten.

Then connect the camera (memory card) to a PC or Mac which has install a data recovery tool, check this site Digital Camera Data Recovery for a list of good and tested recovery software.

Hope you good luck! Merry Christmas!

I had success with asoftech photo recovery program, here's the steps
1. Do not save any new file to memory card.
2. Connect your card to computer. You should see memory card shown as a drive letter (like H:) in My Computer.
3. Download photo recovery software, recommended one is this photo recovery (simply because i was using it and it worked)
http://www.asoftech.com/apr/
4. Install and open the photo recovery program, select your memory drive, and click 'Start' button to start scanning process which will find your deleted photos.

Try take the memory card out of your camera and connect it to your PC via a card reader (as is more secure). Then try this photo recovery software. It should help you out.

WARNING: After accidentally deleting files from a memory card, do not attempt to copy additional files onto the card before attempting file recovery as this will overwrite the files and make them much more difficult if not impossible to recover.

Card Data Recovery is professional photo recovery software to recover deleted, lost, corrupted or formatted photos, videos, and auido files from various memory cards, such as, SDHC card, SD card, CF card, memory card, memory sticks, USB devices, digital cameras, hard drives, and zip drives.

It is quite likely that you will be able to recover the majority of your pictures with an image recovery program. There are many programs available but here is a list of freeware ones:-
http://www.dirfile.com/freeware/photo-recovery.htm

Juts for Sony, esupport.sony.com; if the Memory Stick is of a different manufacturer, then contact them to get the recovery software to recover the files. If the Software is not working, then you may have to contact the Data Recovery firms. For Kodak, try this link: kodak-photo-recovery.

Other posibilitie is take the memory card to a photo store not a big box store because I doubt they would have the necessary software to retrieve the images. What has been done for me in the past is they run there recovery software programing and retrieve in some cases all of the images and in some cases I'll loose one or two random but always over 98% retrieve. Don't format or shoot anything over the images you want to recover.

Hope helps (remember to rate this answer).