Photodynamic therapy, a technique used for several diseases, when carried out in blood vessels, leads to their destruction. However, vessel recovery is observed some time later, which can be an angiogenic process (formation of new blood vessels) induced by the therapy itself or blood reperfusion. For the investigation of this vascular process after photodynamic therapy, the chorioallantoic membrane (CAM) model of chicken eggs was used. Photodynamic therapy was performed on membrane vessels with the Photogem photosensitizer, at a concentration of 10 μg/mL, and light subdoses to avoid leading the embryo to death. Light doses of 6 and 15 J/cm<sup>2</sup> were established for the experiments and a decrease in vessel density 3 hours after photodynamic therapy was observed, with an increase 24 hours later. For quantification of these effects, an equation was determined and a routine of MATLAB was designed to determine the percentage of area occupied by blood vessels in the images, which were performed before, every 30 minutes for the first 3 hours after treatment and 24 hours later. Furthermore, for an analysis of the distribution of large and small vessels, the length and diameter of each vessel in the images were measured with the ImageJ software, which enabled to verify that the smaller vessels are most affected 3 hours after the therapy, with an increase in the number of these vessels after 24 hours.