Last night my internet connection was slow so I canceled Gimp installation (4.5 Mb/53Mb). But today when I try to click on Gimp install button in Ubuntu Software Center, this error came up "Requires installation of untrusted packages". What should I do now?
Close software-center and then open a terminal and run the following command:
Then, open software and try the install again and you should not see the same error.