Specimens of two concretes with different water/cement ratios are subject to various curing and pre-conditioning regimes before being placed in accelerated carbonation conditions. Their carbonation depths are revealed using a phenolphthalein indicator, with image-processing tools used to reduce measurement time, improve accuracy, and eliminate subjectivity of measurements. The results show that specimens cured in water for 28 days show a reduced carbonation depth when compared with those cured in air. Preconditioning with oven-treatment decreased the clarity in the observed carbonation front and had inconsistent effect on the carbonation depth. Image-processing tools were found to be a useful method of consistently measuring carbonation depth using a fixed threshold, particularly in this case where the indication is ambiguous.