1. A system for authoring web pages, comprising: a computing device, having a storage medium storing: a markup language file; and a style sheet file containing breakpoints and a set of image display rules according to which image renditions of a first selected image are generated; a graphics processor configured to: display an image rendition for the first selected image corresponding to the breakpoints, the image rendition having: the first selected image; and crop borders for the first selected image corresponding to the breakpoints; and display a further image rendition that includes modification to the image rendition received by a user input device; the user input device configured to receive an input indicating the modifications to the image rendition; and a processor configured to amend the markup language file with at least one image display rule based upon the further image rendition, the at least one image display rule conforming to the set of image display rules, the processor further configured to present on a user interface via which the user input device receives the input, a first window on the user interface comprising an option to select an image display strategy to be applied to the image rendition, and receive an instruction associated with the image display strategy, the instruction comprising one or more rules for scaling the image within the breakpoints, the instruction saved with the markup language file, the processor further configured to generate a scaled image by applying the instruction to the image rendition, the processor further configured to determine a mismatch between scaled image and the breakpoints, wherein responsive to the mismatch being determined, present on the user interface via which the user input device receives the input, a second window on the user interface comprising an option to select a second selected image, the processor further configured to receive the selection of the second selected image, the processor further configured to replace the first selected image with the second selected image.