c:\@Work\Perl\monks>perl -wMstrict -le
"use Data::Dump qw(dd);
 ;;
 my @matrix = (
   [ qw(A1a1  img1 x123 y123) ],
   [ qw(A21a1 img8 x888 y888) ],
   [ qw(A1a2  img2 x123 y456) ],
   [ qw(A2a1  img9 x999 y999) ],
   [ qw(A1a12 img3 x456 y789) ],
   [ qw(A10a1 img4 x456 y123) ],
   [ qw(A12a1 img5 x456 y456) ],
   );
 dd \@matrix;
 ;;
 sub natural_field {
   my ($field) = @_;
   ;;
   my @fields = $field =~ m{
     \A ([[:upper:]]) (\d+) ([[:lower:]]) (\d+) \z
     }xms
     or die qq{bad sort field: '$field'}
     ;
   return pack 'a N a N', @fields;
   }
 ;;
 my @sorted =
   map  $_->[0],
   sort { $a->[1] cmp $b->[1] }
   map  [ $_, natural_field($_->[0]) ],
   @matrix
   ;
 dd \@sorted;
"
[
  ["A1a1", "img1", "x123", "y123"],
  ["A21a1", "img8", "x888", "y888"],
  ["A1a2", "img2", "x123", "y456"],
  ["A2a1", "img9", "x999", "y999"],
  ["A1a12", "img3", "x456", "y789"],
  ["A10a1", "img4", "x456", "y123"],
  ["A12a1", "img5", "x456", "y456"],
]

[
  ["A1a1", "img1", "x123", "y123"],
  ["A1a2", "img2", "x123", "y456"],
  ["A1a12", "img3", "x456", "y789"],
  ["A2a1", "img9", "x999", "y999"],
  ["A10a1", "img4", "x456", "y123"],
  ["A12a1", "img5", "x456", "y456"],
  ["A21a1", "img8", "x888", "y888"],
]