A computer system image is executed on a computing node over a network. A system specification file transmitted over the network specifies the computer system image by specifying components of the computer system image. The components include an operating system and at least one resource. The system specification file also contains a signature associated with the resource. A resource is determined to be authorized to be incorporated into the computer system image by verifying the signature. A computer system image can then be formed based on the components specified by the system specification file and executed locally.