>perl -wMstrict -le
"my @raw_files = qw{ 12.png 06.png 06.png 03.png 07.png 07.png };
 my $blank_png = 'blank.png';
 my @blanked_files = interleave_blanks($blank_png, @raw_files);
 print qq{@blanked_files};
 sub interleave_blanks {
     my $blank_file = shift;
     my $prev_file = '';
     map {
         my $repeat = $_ eq $prev_file;
         $prev_file = $_;
         $repeat ? ($blank_file, $_) : ($_);
         }
         @_
         ;
     }
"
12.png 06.png blank.png 06.png 03.png 07.png blank.png 07.png

>perl -wMstrict -le
"my @raw_files = qw{ 12.png 06.png 06.png 03.png 07.png 07.png };
 my $blank_png = 'blank.png';
 my @blanked_files = do {
     my $prev_file = '';
     map {
         my $repeat = $_ eq $prev_file;
         $prev_file = $_;
         $repeat ? ($blank_png, $_) : ($_);
         }
         @raw_files
         ;
     };
 print qq{@blanked_files};
"
12.png 06.png blank.png 06.png 03.png 07.png blank.png 07.png
[download]

In case the animation sequence is a continuous loop and thus requires a blank .png inserted after the last .png in the array if the last .png is the same as the first .png, this should do the trick (although it might be a little more elegant without a bunch of reverses scattered all over the place):

>perl -wMstrict -le
"my $blank_png = 'blank.png';
 print qq{\noutput:};
 for (@ARGV) {
     print qq{ in: $_};
     my @raw_files = split;
     my @blanked_files = interleave_blanks($blank_png, @raw_files);
     print qq{out: @blanked_files};
     }
 sub interleave_blanks {
     my $blank_file = shift;
     my $prev_file  = $_[0];
     reverse map {
         my $repeat = $_ eq $prev_file;
         $prev_file = $_;
         $repeat ? ($blank_file, $_) : ($_);
         }
         reverse @_
         ;
     }
"
"12.png 06.png 06.png 03.png 07.png 07.png"
"07.png 12.png 06.png 06.png 03.png 07.png 07.png"

output:
 in: 12.png 06.png 06.png 03.png 07.png 07.png
out: 12.png 06.png blank.png 06.png 03.png 07.png blank.png 07.png
 in: 07.png 12.png 06.png 06.png 03.png 07.png 07.png
out: 07.png 12.png 06.png blank.png 06.png 03.png 07.png blank.png 07.
+png blank.png
[download]

Whoa!!! Where did the original post go? An answer doesn't mean very much without a question.

I personally believe, incidentally, that this is a good reason to include some quote from the nodes I reply to, when I do reply. This is a habit I got from usenet, actually, and it has been often debated here, with good arguments both in favour of doing so and against. To be fair, at least as of late, I generally don't follow it myself, when commenting such short nodes as yours here or when it's clear that I'm replying to the whole node anyway, whereas I more closely stick to it when I want to stress the single points I'm addressing.

--
If you can't understand the incipit, then please check the IPB Campaign.

gringocharlie, please re-update your post to include what you posted originally. As it stands your post is useless to people having the same problem.

For future reference, a good convention is to add any updates to the end of the post (without deleting the original content!) and prefix the update with the word 'update:' in bold.