just trying scm-manager as a git server and after some test I find it very great. But, I got my images file not display by default in the web-interface. Thought it would be very very nice to have it displayed correctly as image. Is this need a plugin? Or, how can I tweak this? Any clue would be really appreciated.
Actually this is not possible. You can click at the "Raw" button at the content viewer to download the image.
If you want to implement this feature, you can fork the project at https://bitbucket.org/sdorra/scm-manager/ and override the openFile method in the file sonia.repository.repositorybrowser.js to open a imagePanel instead of a contentPanel if the path refers to an image file.
If you don't want to implement this by yourself, you can make a feature request at https://bitbucket.org/sdorra/scm-manager/issues.