Disclosed herein are systems, methods, and non-transitory computer-readable storage media for a delayed secure deletion of files from a copy-on-write file system. 0 to 100 mmsec; wherein the light-sensitive material to be exposed contains any of: 1) a dye-forming coupler of formula, 2) a compound of formula, and 3) 1. The sampling clock control unit is configured to generate a delay control signal and a synchronization completion signal in response to the plurality of internal data signals and a first group of clock signals.