my $line = 'The quick <CM>HTMLINSERT:<img src="grab me!"></CM> brown fox';
my $key  = '<CM>HTMLINSERT:<img src=([^>]+)></CM>';
my %fsr_hash;
$fsr_hash{$key} = '"<figure><graphic url=$1/></figure></p>"';

$line =~ s/$key/$fsr_hash{$key}/gee;

print "$line\n";