Never Delete Images from your Memory Card in the Camera

I found these very interesting comments on a forum which I visit with respect to deleting images from your memory card while out shooting.  I have permission from the author to reproduce it here.


When I worked for Kodak, they absolutely insisted on two basic principles:

• Do not ever, under any circumstances, delete ANY images in-camera. They were so insistent on this that it was a sacking offence to do so (and, yes, they did check every job). The point was that assessment of images on the small camera-back screen has a number of inherent drawbacks:
  

1. Irrespective of the shooting mode, the camera-back image is a JPEG processed with camera default settings. It bears only a passing resemblance to the RAW image actually shot.
2. The resolution camera-back is so relatively low that detail is often simply not visible. This detail may be important.
3. There is no way on earth that we could accurately assess anything on a 3" diagonal screen which would subsequently be viewed on a 27" diagonal screen.
4. An apparently 'duff' shot may not be usable in it's own right - but it may be a source for cloning to improve a different shot. (Think of cloning open eyes from a duff shot onto a better shot which suffers from closed eyes.)
5. So-called 'Chimping' is best left to the experts - the Chimps. Useful for checking for closed eyes / nice smiles but very little else in terms other than sheer curiosity. No monkeying around!
   

• Only ever format the card(s) IN-CAMERA.
  

1. Different cameras (even within the same marque, different eras) have different ways of organising the data. At that time (and possibly still, to this day), many but not all cameras used a 12-bit FAT. This was not always compatible with the computer OS - some 16-bit, some 32-bit, now many don't even use a FAT as the camera knows it. Format in computer, while very tempting, may lead to unusable cards. Plus, it's logical to format in the equipment being used to record subsequent images.
2. Different brands of card could occasionally throw up compatibility problems with certain cameras. We had a fair number of difficulties specifically with Lexar cards in Canon cameras and settled on SanDisk as being the most reliable brand - or, rather, the least unreliable!
   

Since those days, I have always worked on those two principles (with a third one of never shooting any job on less than 4 cards - simply to spread the risk of loss). One problem with digital is that anything other than a full capture tends to be completely blank - with film there was at least something which could be rescued in some form.
Perhaps it's a matter of supreme caution but adhering to those two basic principles will come as close as possible to guaranteeing results. You may 'get away' with a less rigorous technique - but then again you may not. Why take the risk?