It is only in the case of the Red Scapular that the images are expressly prescribed. Scapulars are available free from the Carmelites. Kits for home sewing are available from the Carmelites, with all the materials, at less cost. You could consider this as an apostolate to make the finished product available in your parish bookstore. According to Father John Hardon's Catholic Dictionary the scapular medal was authorized as a substitute by Pope Saint Pius X in 1910.
Investiture requires the scapular.
After that the medal may be worn for any reason even for reasons of convenience. The scapular medal has all the same indulgences that are associated with cloth scapular. The cloth scapular must be worn around the neck, with one tab in front and one in back, inside or outside the clothing, but medal can be worn anywhere on the person, including in one's pocket. Many rosaries have scapular medals on them. If you are enrolled in the brown scapular, carrying that rosary in your pocket is the same as wearing one around your neck.