The images taken with the Snapmatic app on the in game phone are saved to your computer but are not viewable on a regular Windows machine. It is possible to open the image in an image editor like Photoshop and re-save it as a regular image file, but this utility will do this for you.
Please note that the images appear to be saved at a 960x536 resolution.

How to use

• Navigate to your GTAV profile folder. Usually located at C:\Users\<USERNAME>\Documents\Rockstar Games\GTA V\Profiles\<PROFILEID OR SOMETHING>
• Find the image you wish to convert. Images start with PGTA and then some random numbers and no file extension (ex. PGTA51182301695)
• Drag the image(s) to the converter icon
• The image will be saved to the same location as the original file but with a '.jpg' extension
  

Manually fixing the image
To manually 'fix' the image you need to have a HEX editor and some knowledge of using it.

• Open the image in a HEX editor
• Look for the bytes sequence FF D8.
• Delete everythign before the FF byte.
  I found the FF byte is at offset 124, so delete everything up untill that offset.
• Save the file and add a .jpg extension (since it is a jpg file)
  
  

Notes
Future game updates may break this utility.
Currently tested with version 1.0.231.0