We take photos of everything now; sometimes too much. Having the freedom of digital cameras means that it's even easier to take photos anywhere and everywhere, and to take lots of them. Unfortunately it also makes it easier to lose a photo seemingly forever.
Thankfully you don't need fancy technology or IT-know-how to recover those lost images of your trip to Paris.
Time: Depends how big your memory card is
Materials Memory Card (and memory card reader)
First, and this might sound a little stupid, just make sure you haven't 'misplaced' the photos. It's happened before. You've searched for photos on an SD card only to realise their on the one that's sitting on the desk in your study not the one in your camera. Or you've downloaded photos onto your computer, but you didn't download them to the place you should have and now you're convinced they're lost forever. Check and double check all the likely places the photos can be. There's no point panicing if they're just sitting in another section of your hard drive.
They're gone? Now it's time to find the memory card they were on and connect it to your computer. Most programs need the card connected directly, so if you don't have a built in card reader you'll need to buy one.
Download a recovery program. You can get programs for both Windows and OSX, and a lot of them are free. A few to try are Recuva, PhotoREC, Exif Untrasher, Pandora Recovery, and Recover Files. Each program works differently, so once you've downloaded and installed the program just follow the prompts.
Wait. Depending on the amount of photos your card may be holding, the process can take a while. Make yourself a cup of tea. Paint your toenails. Start to breath a little after the initial panic of losing all your photos.
Hopefully by now your chosen program has worked it's magic and you should have a folder with all your deleted files.