I spent a few hours trying to get my camera working with my raspberry pi 3, the errors I was receiving are illustrated below.
I was silly enough to have connected it to the wrong port, but it seems to be a common issue as there are two connectors that are a similar size.
I have attached an image which show which port the camera should be connected to.
raspistill -o image.jpg
mmal: main: Failed to create camera component mmal: Camera is not detected. Please check carefully the camera module is installed correctly<code><br></code>
Above are the error and below is an image of a raspberry pi which shows all the connectors locations.