digiKam from KDE3 branch : Camera Gui : always download the current picture as temp file before to check if target file already exist in target album. The advantage of this way is simple. We can always show a preview of picture from camera because file is in local file system. Also, this way work with all camera type (gphoto2 include).

Important remarks : The Rename dialog is provided by KDE api (KIO::RenameDlg class).
- With KDE 3.4.x, this dialog is not able to display preview of pictures properlly.
- With KDE 3.5, the dialog have been revisted, work better, but sometime the preview doesn't work properlly with JPEG, and PNG files. It's never work with RAW file.
This is duing of limitation in picture preview implementation provided by KDE API.
I have not yet tested with KDE4.

Possible solution of this problem is to use digiKam core to render preview. But we must fork KIO::RenameDlg for that, which is a wrong way.

I recommend to post a new report in KDElibs to improve definitivly the pictures preview implementation to work properlly in all cases.