Despite the rising popularity of tattoos, demand for their removal has also increased. Tattoo removal is mostly treated by laser. But it requires repeated treatment, and the single curative effect is not accurate enough by visual examination. This article mainly studies the quantitative evaluation of treatment effect based on image technology. Tattoos were made on the pigskin with different colors, then we used a picosecond laser set at various energy parameters to remove the tattoos. The images of the treated area and normal skin tissue were collected, and the extracted area was standardized. After extracting features, the area ratio of tattoos before and after irradiation was quantified, and then the removal rate was obtained. In order to verify the reliability of the quantization algorithm, standard images with different contrast are designed to calculate the proportion of pigment, and the errors obtained are all less than 0.01%, which proves that the algorithm is reliable. The quantitative evaluation of pigment removal can objectively reflect the effect of laser pigment removal, and avoid the deviation of curative effect caused by subjective judgment. This study provides great help in selecting laser treatment parameters and improving the efficacy.