for the last question:
the first script (html) writes:

print q{<img src="/cgi-bin/imgserv.pl">};
...
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the second script (imgserv.pl) writes:

# suppose you have read() an immage into $image_data
# and image type is jpeg...
print "Content-Type: image/jpeg\n\n";
binmode STDOUT;
#just if you are unde windows 
#not needed on more serious platforms :-)
print $image_data;
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