Note: These steps are no longer needed, as the latest version of Skype now loads virtual camera. Updating Skype should be all that's required to see virtual cameras in Skype.
On some systems, the Terminal workaround for Skype cannot make the necessary changes to Skype in order to allow virtual cameras to load.
If you followed Option #2 in the article about, and received error messages, you can use these steps to fix the problem.
Open Terminal (in Application/Utilities)
Copy and paste this command and press return.
sudo xcode-select --install
3. Follow the prompts to enter your computer's admin password. You won't see your password as you type it. Press return when done entering the password.
NOTE: If this command gives an error message about "command line tools are already installed", copy and paste this command and then press return:
sudo xcode-select --switch /Library/Developer/CommandLineTools
4. Copy and paste this command and press return.
sudo xcode-select --reset
5. Then, be sure to run the codesign command from the previous article again.