By "unprocessed" you mean not turned into the movie yet? Or nothing that requires manual attention and interaction?
If you will be cropping, crop the stills early.
The video (if normal video usage; you did not specify) is much lower resolution than a photo. So resuce the resolution to the final dimentions, right away.
You say these are in-camera jpeg files, so they are already small. Get another hdd, valuing price over performance. Last week they were running $30/Terabyte.
- You could start forming the movie before you hace all the shots. Each group, say 1 seconds worth, can be formed into a video. Then, paste them together.
Note that anything you do might result in lost quality unless you are very careful and know what you are doing. You will also lose flexibility; e.g. you might wish to reframe once you are editing.
For real savings, making each run of 24 frames (or whatever) into a movie right away is the only real approach. If you finish it the waynthe movie will be, you are no worse off since you are not saving intermediate forms. And really, you need the space for the finished movie anyway!
If each run corresponds to a "group-of-pictures" in the final video encoding, and you find the right tool you can concatenate them together without any re-encoding (which would be generational loss).
Really though, if an in-camera jpeg is 5Mb it would take 200,000 images to fill a terabyte, which would be enough to make a 55-hour movie. So can you detail just what your space issues are?