IPC-HDBW4431R-ZS snapshot, [M]xxx.jpg and [F]xxx.jpg

[digital_v]

Hello!
I have 2 cameras Dahua IPC-HDBW4431R-ZS, I need to get snapshot from them. The main way to get it is Linux:
curl --digest --user loginass "http://$IP/cgi-bin/snapshot.cgi" -o $OUT/$name.jpg.
After this command, I get 2 files: 28[M][0@0][0].jpg, and 28[F][0@0][0].jpg. Is it a camera feature or an error in the firmware, how do I get one file?

 

[alastairstevenson]

Maybe [M] medium and [F] fine resolution?
What are the file properties?

 

[digital_v]

The files are absolutely identical, the resolution and size are the same.
If the file jpg is sent by the camera itself (the motion detector has triggered), then the file in a single - [M]xxx.jpg