vector_normalized_distance varies depending on size of image

[357r4bd]

A user of my Perl module, Image::Libpuzzle has created an issue for my repo of the same title.

357r4bd/Image-Libpuzzle#5

I can reproduce it using puzzle-diff, so it is not an issue with my module (itself a wrapper around libpuzzle).

I am using libpuzzle-0.11 on OSX. I am not sure what OS/lib version the reporter of the original issue (above) is using.

Attached are the images and a script to demonstrate the issue. The script used to generated the scaled versions of the original image is also included (generate.pl).
issue-files.zip

Below is 2 sets of output, one using my module (compare.pl) and a shell script using puzzle-diff (compare.sh):

Using Image::Libpuzzle:

$ ./compare.pl
100: 0.634182997760008
200: 0.61913918736689
300: 0.0698092831405639
400: 0.604140770698438
500: 0.62196043417488
600: 0.0420496681819964
700: 0.605117883422495
800: 0.622808505614176
900: 0.0419672983694311
1000: 0.606714082142257

Using puzzle-diff:

$ ./compare.sh
100: 0.634183
200: 0.619139
300: 0.0698093
400: 0.604141
500: 0.62196
600: 0.0420497
700: 0.605118
800: 0.622809
900: 0.0419673
1000: 0.606714

Please advise. Thank you.

[357r4bd]

Additional analysis of the issue. See point 2 in the link below.

https://rt.cpan.org/Public/Ticket/Attachment/1636164/876996

See https://rt.cpan.org/Ticket/Display.html?id=113716#txn-1636164 for referenced scripts.