How to recover CM Security Hidden photos in .cms file format?

Registration date
Tuesday August 22, 2017
Last seen
August 22, 2017
- Aug 22, 2017 at 12:45 PM

I had my sony xperia m4 aqua broken when I accidentally stepped on the screen. I had som many important screenshots of my email account and including private photos on my vault. I tried to remove the sd card and inserted it on my laptop. I can the files in there. But the thing is, I cannot open them. When I tried to change the file extension into .jpg, .png the only thing that is displayed is the cm security logo. Is there any way I can retrieve these files? Can anyone help me with this? Need I to download any software?
Any help would be much appreciated.
thank you!