A markup element of a markup language document references a resource with a resource indicator. A method for verifying the content of the resource includes extracting a characteristic of the content from the markup element, retrieving a resource according to the resource indicator, and comparing a characteristic of the content of the retrieved resource to the extracted characteristic. A computer readable program for authoring a markup language document when executed on a computer causes the computer to include in a markup element of the markup language document a characteristic of the content of a resource that is referenced by the markup element with a resource indicator.