A method is provided for controlling access to a protected resource in a computing system, which includes storing an indication of a selection of an access image type, receiving an access request for accessing the protected resource, and determining one or more access locations of an access grid of images, the access locations (and possibly the corresponding images) changing along a sequence of access requests. The method also includes generating the access grid to include corresponding access images of the access image type for the access locations and one or more other image types different from the access image type, displaying the access grid, and controlling the access to the protected resource according to a selection of one or more selected images in the access grid.