The free service with CameraFTP is only meant for testing compatibility. To upload and store camera footage, a paid subscription will be required.
Now with regards to the limits of your DVR, this is not something that CameraFTP will be able to do much about. If your DVR does not support image (snapshot) upload, CameraFTP would not have a way of forcing this change. One suggestion depending on your physical cameras capabilities would be to remove the DVR from the equation and configure your cameras to upload to CameraFTP directly. This is the standard way of using our service.
Please feel free to email email@example.com if you have any other questions.