(Slightly OT) What is the best way to read images from a DSLR attached to a Pi via USB? I'd like to build a simple timelapse system where - the image taking

(Slightly OT) What is the best way to read images from a DSLR attached to a Pi via USB? I'd like to build a simple timelapse system where - the image taking is done via the remote cable attached to GPIO pins of the PI - each image, when taken, is sent to the Pi via USB (RAW+Jpeg) for processing, upload, etc. The first part seems fairly easy, but the second part not so much. Any pointer appreciated.