I take a lot of pictures. My camera records the pictures to an SD card. I then transfer the pictures I want to keep to a computer. I have several SD cards and I used the one most handy.
Over time, I had several cards with similar data which should have been grouped together. I made a folder on my desktop and named it 'From SD cards-To be sorted'. Then I transferred all the data from all the cards to this folder. That left all my SD cards 'empty'. At least that's what Windows said.
I started anew with one card and began taking pictures again. I had accumulated about 50 pictures on the card when I made a mistake. I accidentally deleted a picture. My intention was to rename the file. The 'Rename' and 'Delete' options in my context menu are one after another, so I make this mistake often. There is a free software that allows you to reposition the context menu options. I plan to download it and make use of it. Most deleted files are easily retrievable from the Recycle Bin. However, files from SD cards are simply deleted. They are not sent to the Recycle Bin.
The picture I deleted was one I had planned to submit to ThriftyFun and I did not have a copy. I went to the Internet and found several software for recovering data deleted from SD cards. I picked one that was free. It was an excellent software, very easy to use. It did have limitations in that it would only retrieve 1 GB of data for free. That was OK. A Gig is a lot of pictures and I was only interested in retrieving one among about fifty.
In very short order, the software retrieved not only the picture I accidentally deleted but hundreds more, hundreds I had 'emptied/deleted' from the card. All the pictures I had taken and deleted were still on the card. Had I not recently taken 50 more pictures, my computer would have shown the card as 'Empty', while this software showed it to contain hundreds of files.
If you have data stored on an SD card that you do not want to fall into the wrong hands, I can tell you, deleting the data is not enough. It is still retrievable, often even after the card has been reformatted.
There are free software available said to reformat an SD card in such a manner no data can be retrieved. We'll save that for another post.
Summation: When you think you have deleted all data from an SD card, you actually have not. If the card once held sensitive data, it more than likely still does. It would be wise to keep these cards in a secure place. And if you happen to give someone an 'empty' used card as a gift, do know that any data you once put on that card could still be retrievable.
Unless you are 'tech savvy' on 'wiping' SD cards, and they do happen to contain sensitive data, keep them secure or destroy them.
This is good to know as making a mistake like that can happen anytime so I'm glad to know there are programs to retrieve the deleted files (even free!). We have been using the same SD cards for a long time and we tend to buy new cameras that use the same type cards but it is good to know that we should destroy them if getting rid of one.