You need to output HTTP headers indicating a proper Content-Type for a PNG image. Before the binmode, you want something like

print "Content-type: image/x-png\n\n";
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---
print map { my ($m)=1<<hex($_)&11?' ':'';
$m.=substr('AHJPacehklnorstu',hex($_),1) }
split //,'2fde0abe76c36c914586c';
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