Physical examination on a 65-year-old man with mild congestive hea failure reveals varicose veins, ankle edema, and inflammation of much of the skin near the ankles of both legs. The affected skin exhibits edema, erythema, mild scaling, and brown discoloration. The edges of skin involvement are poorly defined. On one ankle, a one centimeter diameter ulcerated area is seen within the erythematous area. The patient says that his leg lesions look much worse than they feel. Which of the following is the most likely diagnosis?