Secure Access by a User to a Resource

In a method of approving access to a server network from any terminal requesting access, a communication request is sent from the terminal to a server on a first communication path. An image containing a series of symbols is communicated to the user on a communication path different from the first path. From the image the user calculates a response based upon a particular pattern in the image defining certain symbols which are then used in an operation to determine from the symbols a response which is different from the symbols. A comparison is made between the response received and a previously stored response to assess whether access should be allowed.