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sudo add-apt-repository ppa:philip5/extra

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sudo apt-get update

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sudo apt-get install digikam
sudo aptitude install digikam
###   Not Installed, but Recommended ffmpegthumbs kipi-plugins mplayerthumbs

To add themes, you will have to install an extra pack­age (as decribed here) like this:
sudo apt-get install kde-workspace-data