There is only one file type that uses the .KSD extension:
Security file created by KeepSafe, a mobile application that enables you to "lock" or "hide" your images and video; contains a video or image that is hidden from the user until the appropriate pin is entered.
Locked files are contained in the following directory:
KeepSafe\Documents\Media\[Album Name - default album is Safe Roll]
After you choose a video or image to be hidden, KeepSafe appends a string of numbers preceding the filename and the KSD extension on to the end of the file. The extension hides the file from being recognized as the file it really is, such as a .JPG file, and prevents the device from showing the file.
For example, KeepSafe may save an image file as 4743615774357373042.IMG_1247.JPG.KSD. The "4743615774357373042" is a random string of numbers generated by KeepSafe and "KSD" is the extension added by the program.
NOTE: The KSD extension replaced the .HID extension in 2013.
Updated: September 5, 2013