There are various EXIF tools around of course, but simplicity is always a plus.
This approach might not work for some brands that omit the value, but it’s easy for the Leica M9 (see also the method I used back in 2006).
- Open an image in Photoshop or any program that can display the raw EXIF info (on OS X, Apple Preview has a Get Info that will show the info).
- Find the number. This number is in hexadecimal (base 16).
- Convert the hexadecimal number to base 10. On the Mac, the built-in Apple calculator in programmer mode has buttons for this as shown below (8/10/16).
In this particular example, hexadecimal 0x0001519 is decimal 5401.
Many cameras do not have this info readily evident; it might be a different tag and/or deliberately obfuscated.
- The Nikon Coolpix A has a field “<aux:ImageNumber>242</aux:ImageNumber>” which appears to be the same, but I’m not certain.