Functions which return objects sometimes marked as returning resources

[shish]

eg imagecreate is marked as returning a resource when it actually returns a GdImage - #533 fixed this for function parameters, but didn't fix it for function return types

[dmecke]

Thank you for looking into this. The docblock of the image.php in the generated folders also state that it might return false - which is not true as the case is handled with an exception.
Sorry, if this was already obvious, I'm not too well aware where the project pulls its type information from.