Because FileZilla doesn’t upload some images for some reason, and gFTP sometimes complains that “transport endpoint is not connected”, and I couldn’t for the life of me get ncFTP to recursively download an entire directory correctly, I switched to lFTP. This program has a peculiar way of uploading and downloading entire directories, though. For future reference:

lftp -u
mirror crashkurs  # recursive download
mirror -R somedir  # recursive upload