"Giving your photos meaningful names makes it significantly easier to keep tabs on them. Of course, renaming each and every photo by hand is not particularly practical, especially if you take dozens or even hundreds of photos each day. This is when digiKam's Rename feature can come in rather handy. You can use it to define rather advanced renaming rules and apply them to multiple photos in one fell swoop.
"To put the Rename tool to practical use, select the photos you want to rename and press the Rename button in the main toolbar (you can also choose Image | Rename or press F2). The Rename dialog window offers a vast range of renaming options which allow you to create complex renaming rules. But you might want to start with a simple rule that renames photos using the date and time data. To do this, press the Date & Time button and select Image from the Source drop-down list. This will pull the date and time info from the photo's metadata."