Nowadays, more and more digital images are being sent over computer networks. The works presented in this chapter show how encryption and watermarking algorithms provide security to medical imagery. In order to do this, the images can be encrypted in their source codes in order to apply this functionality at application level. In this way, the encryption and watermarking of images occurs at software level. We can therefore guarantee the protection of a medical image during transmission, and also once this digital data is archived. The subsequent challenge is to ensure that such coding withstands severe treatment such as compression. The quantity of information (entropy) to be sent greatly increases from the original image to the encrypted image. In the case of certain types of medical imagery, large homogenous zones appear. These zones affect the effectiveness of the coding algorithms. Nevertheless, these homogenous zones, useless for any diagnosis, can be safely used for the watermarking of medical images. When a physician receives a visit from a patient, he often requires a specialist opinion before giving a diagnosis. One possible solution is to send images of the patient, along with a specialist report, over a computer network. Nevertheless, computer networks are complex and espionage is a potential risk. We are therefore Chapter written by William PUECH and Gouenou COATRIEUX.