The characteristic of paper absorbing ink phenomena in offset printing was analyzed. Using image analysis method, area spot ratio, edge raggedness, and roundness degree which can indicate dot fidelity were tested. Image-Pro Plus 6.0 software was used to process digital image to get data. Through the data analysis of four kinds of coated papers, dot fidelity of offset printing was evaluated. This method was proved to be feasible and usable by comparing with the result of density and colorimetric values.