This study further researches the relationship between the exposure and development time using an automatic inspection system, and the relationship between the development time and photoresist depth. This progressive scan camera with 233 frames per second in partial scanning mode was used to obtain the photoresist development processing parameters. In this real-time imaging system, we calculate the image contrast for the exposed area and non-exposed area to find the optimum development time. When the database is adjusted, the thickness prediction error for the on-line inspection is retained to within 4%. The image-based measurement application with unsophisticated and economical equipment is confirmed in the photo etching processing.