When you delete a a photo, word document, excel document etc, by default the file is placed in your recycle bin. You then empty the recycle bin and the data is permanently removed, or is it??
When you empty your recycle bin the operating system does not really remove the file from the disk but only removes the reference of the file from the file system table. The file will remain on the disk until another file is created over it, but even after that it might be possible to recover data by studying the magnetic fields on the disk platter surface.
There are lots of tools available on the net free and paid which allow you to overwrite your deleted data multiple times so their inaccessible.
One of the tools out there is Eraser, a free tool which can be downloaded from here
I found this tool easy to use and did a good job
1) It works with Windows XP (with Service Pack 3), Windows Server 2003 (with Service Pack 2), Windows Vista, Windows Server 2008, Windows 7 and Windows Server 2008 R2
2) Windows 98, ME, NT, 2000 can still be used with version 5.7
3) It works with any drive that works with Windows
4) Secure drive erasure methods are supported out of the box
5) Erases files, folders and their previously deleted counterparts
6) Works with an extremely customisable Scheduler