A device and method for compressing image data. Image data is received comprising one or more images recorded by a camera. Attitude data is received indicating the attitude of the camera when each of the one or more images was recorded. In each of the one or more images, a region of interest is defined, the region of interest being bounded by a boundary, the boundary of the region of interest being based on the attitude data for the respective image and defining a section of the image within the region of interest and a section of the image outside the region of interest. Each of the one or more images is compressed, wherein the compression ratio applied to the section of the image outside the region of interest is higher than that applied to the section of the image within the region of interest.