Which doesn't seem to work very well as I'm getting some rather strange output. TIA.

Such as?

Parsing html (which is what you're trying to do) with regular expressions is hard (more so when you're green). But as usual, there is always CPAN (HTML::StripScripts::Regex, YAPE::HTML )

use Regexp::Common qw /delimited/;
my $text = q~
qqq <img   src  = "src"  >
sss <img   src='src' >

~;
$text =~ s~
         img \s+ src
        \s* \= \s*
        (?: $RE{delimited}{-delim=>'"'} |
            $RE{delimited}{-delim=>"'"}
        )
         ~bongo~sigx;
print $text,$/,$/;
__END__

qqq <bongo  >
sss <bongo >
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