Abstract: A camera 1 comprises first and second camera systems 3, 5. The first camera system 3 is a high resolution camera which captures images (so-called ‘key frames’) at a relatively low rate, whilst the second camera system 5 is a low resolution camera which captures images (so-called ‘video frames’) at a higher rate. Accordingly, a plurality of video frames are captured between each key frame. An application program is provided, either in a PC 13 to which the frames are downloaded, or in the camera 1 itself. The main purpose of the application program is to decide which of the captured frames should be stored, and which should be discarded (i.e. by a deletion or replacement operation) thereby freeing-up memory.