NiosII

You will either have to find or implement a different file system with write access, or use another method. For example instead of a file, you can put the JPEG data in a table or an allocated memory buffer and re-read it from there.

An alternative is to use the host file system instead of the rozipfs, and then you can directly read/write files on your PC. But this will only work when running the application with the debugger, not if you directly execute it.