No dpi in exif set = 96dpi in Windows

[Donaufisch]

Hello,
If there are pictures with no dpi set in its metadata, Windows shows the value "96dpi". Actually I am looking for a simple routine to find whatsapp pictures on a big backup hdd. Therefore I want to use the Windows calculation to find all 96dpi pictures, because all Whatsapp pics have that 96dpi.there is only the resoulution stored in these pics. All other information is deleted by Whatsapp.

If there is nothing else set then the x and y resolution, Windows has to usw the resolution  to calculate that 96 dpi value.
With exiftool I can extract the resolution as well. So all I need is the formula that gives me the 96 dpi.

can you help?
 

[Phil Harvey]

Do you mean something like this?:

exiftool -if "not $xresolution or $xresolution == 96" -filepath -s3 -r DIR

this will list all files with no resolution info or 96 dpi.

- Phil