Assuming that you're looking for every image name within the file:

# On the commandline
 perl -0wne'print "$_\n" for /img\s+src="([^"]+)"/igsm'  filename
[download]

If you're doing this within a script:

# Since HTML tags can be split into multiple lines, you need all the
# content as one string
open Fh, "<", "filename" or die "filename: $!\n";
my $file = do { local $/; <Fh> };
close Fh;

for ($file =~ /img\s+src="([^"]+)"/igsm){
    print "$_\n";
}
[download]

Update: Whoops, I appear to have misread what was being asked, and gave a solution to something different. As JavaFan said, the right answer is to use one of the available modules.