Digital image analysis was applied to the products of simple colour presumptive tests for opiates. Adobe Photoshop software was used for colour analysis to obtain analytical data in the form of a Red Green Blue (RGB) value. Calibration curves were developed for morphine, codeine, and diamorphine hydrochloride and the developed tests successfully applied to seized heroin samples to demonstrate the application of the technique in a forensic case context. Good agreement with gas chromatographic quantification results was obtained for the illicit samples analysed and a wide linear range and low detection limit for all drugs under test facilitated the application to illicit samples. The results show great potential for use as a semi-quantitative field test for illicit drug compounds.