1) First of all install cheese (to normally use your webcam). In a terminal type the command:
Then launch the program with the terminal (typing cheese) or using the menu Applications > Audio and Video. Do you see the webcam working? If not, there is something wrong (maybe with the webcam drivers, etc.) and you have to fix it first. If webcam works you can normally use cheese and you can set the correct resolution in Modify → Preferences → Resolution.
Then you have to modify the config.xml file:
Where the numbers refer to the resolution you previously set in cheese. Save, exit, restart Skype and click on Try in Main menu → Options → Video device. Now your webcam should work properly also in normal videocalls.
2) Another way to fix the webcam is to launch Skype with this command (which include a library):
Check if the webcam works clicking on Try in Main menu → Options → Video device. If it doesn't work the problem is another. If it works you can set the default launcher in the menu Application in this way. Create a text file just with the command above. Rename it skype_launcher.sh, copy it in /usr/share/applications/:
Set execution permissions:
Then open the configuration file for the icon Skype in the Application menu:
You will see something like that:
Modify only the Exec row in this way:
Save, exit, restart Skype using the icon in the Applitation menu and click on Try in Main menu → Options → Video device. Now your webcam should work properly also in normal videocalls.