The traffic of digital images has grown rapidly in the Internet. Security of image becomes important for many sectors mainly for medical applications. Nowadays, the transmission of medical images is a daily routine, especially over wireless (battlefields, traffic accidents, etc). Partial encryption is an approach to reduce the computational resources for huge volumes of multimedia data in low power network. This paper presents a method of partial or selective encryption for JPEG images. It is based on encryption of some quantified DCT coefficients in low and high frequencies. We have combined compression and encryption in order to fully dissimulate the visual information of the image and to see the image in low quality resolution.