use strict;
use warnings;
use Image::ExifTool qw(:Public);
use Date::Calc qw/Date_to_Time/;

my $imageDir = './images';
my %timeFiles;

### Read each file's EXIF info and convert to seconds
### A Hash of Arrays (HoA) is used in case images have the same time
for my $image (<$imageDir/*>) {
	# Skip image if no DateTimeOriginal info (highly unlikely)
	next unless my $dateTime = ImageInfo($image)->{DateTimeOriginal};
	# Convert 'YYYY:MM:DD HH:MM:SS' to seconds
	my $time = Date_to_Time( split /[:\s]/, $dateTime );
	push @{ $timeFiles{$time} }, $image;
}

### <roboticus code>
### Sort the times from the hash
my @times = sort { $a<=>$b } keys %timeFiles;                    
      
### Group together the pix whose time is less than MAX_TIME_DIFF seconds
### apart
my $MAX_TIME_DIFF=10;  # Minimum time between photos
my $MIN_GRP_SIZE=3;    # Minimum "interesting" group size
my @groups;         
my $cur_group = [ shift @times ];                    
      
while (@times) {    
    if ($$cur_group[-1]+$MAX_TIME_DIFF >= $times[0]) {           
        # small interval, add to current group       
        push @$cur_group, shift @times;              
    } 
    else {
        # store last group (if interesting) and start
        # a new one.
        push @groups, $cur_group if @$cur_group >= $MIN_GRP_SIZE;
        $cur_group = [ shift @times ];
    } 
}
### </roboticus code>

### Get each group
for my $group(@groups){
	# The time in each group
	for my $time(@$group){
		# The hash value is an array ref
		# $_ takes the value of each array element, viz., a file name
		print "$_: $time\n" for @{ $timeFiles{$time} };
	}
	# Print blank lines between groups
	print "\n\n";
}

##</code><code>##

./images/IMG_7139.CR2: 1336823075
./images/IMG_7140.CR2: 1336823077
./images/IMG_7141.CR2: 1336823079
./images/IMG_7142.CR2: 1336823082
./images/IMG_7143.CR2: 1336823084
./images/IMG_7144.CR2: 1336823086
./images/IMG_7145.CR2: 1336823088


./images/IMG_7152.CR2: 1336823437
./images/IMG_7153.CR2: 1336823442
./images/IMG_7154.CR2: 1336823446
./images/IMG_7155.CR2: 1336823451
./images/IMG_7156.CR2: 1336823455


./images/IMG_7157.CR2: 1336823467
./images/IMG_7158.CR2: 1336823470
./images/IMG_7159.CR2: 1336823473


./images/IMG_7160.CR2: 1336823653
./images/IMG_7161.CR2: 1336823657
./images/IMG_7162.CR2: 1336823661
./images/IMG_7163.CR2: 1336823664
./images/IMG_7164.CR2: 1336823667