$ cat t.pl
#!/usr/bin/perl     
use strict; use warnings;                            
use Data::Dumper;   

### Get a list of picture times, in seconds      
my @times;
push @times, int 150*rand for 0 .. 30;               

### Sort them
@times = sort { $a<=>$b } @times;                    
      
### 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 ];
    } 
}     
      
print Dumper(\@groups);

$ perl t.pl
$VAR1 = [
          [
            32,
            36,
            39,
            39,
            40,
            42,
            48,
            53,
            55,
            56,
            57,
            58,
            59
          ],
          [
            72,
            73,
            77,
            82
          ],
          [
            93,
            103,
            104,
            105,
            108,
            111,
            113,
            113,
            114,
            116
          ]
        ];