Hi, Alf,
I have a couple of suggestions for you to try. First, double-check (with the Synaptic Package Manager) that you have the following packages installed on your system:
thunar-volman
xfce4-volstatus-plugin
xfce4-mount-plugin
There is some good information in this thread; it might point you in the direction of a solution:
http://www.pclinuxos.com/forum/index.php/topic,78531.0.html"
[SOLVED] Fujifilm AV100 not being recognised." 26 Aug. 2010.
If none of these ideas work, it would be helpful for you to post some additional information, such as:
Can you successfully mount a USB thumbdrive on your system?
What is the specific model of your Canon camera? (Maybe its owner's manual will give you instructions on how to configure it so that it can upload photos to a computer).
If you don't already own a USB card reader, I'd recommend purchasing one. They are very inexpensive now, and they make uploading pictures from the camera so much easier / faster, that I never want to go back to doing it the "old-fashioned" way unless there's no alternative ...
HTH,
=david