Hi,
The negative is a must as they will have to keep the same while they do the x-ray with your name and negative in one corner. There is no alternative.
Many studios know this procedure and they keep film cameras as well to fulfill this requirement. What they do is give you a photo print from the digital camera and take another snap immediately after you digital photo capture and develop and give it to you.
Yes, the DMP will discuss if there are any issues w.r.t the check ups. They may ask for a re-test/resample if the result is positive or not clear sometimes, which are very remote. They may not know what is acceptable to CIC/CHC. The DMP told me that if there is any problems in the result, then they will inform the patient accordingly as per their ethics.
No need to worry. Just pray to GOD and proceed for medicals.
All the best.
C Lad