Would the diagonal diameter work? 
#!/usr/bin/env perl

use strict;

# identify -format "%h:%w" image.png
# 774:423

my $width = 423;
my $height = 774;

my $diag = sqrt( $width**2 + $height**2);

print $diag, "\n";

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In reply to Re: Dealing with rectangular images by mhearse
in thread Dealing with rectangular images by htmanning

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