Just have a CGI (or other server-side Perl script) that, when called, outputs HTTP headers and content:

my $jpeg = getTheJpeg();
binmode STDOUT;
print
  "Content-Type: image-jpeg\r\n",
  "Content-Length: ", length($jpeg), "\r\n\r\n",
  $jpeg;
[download]

The CGI is then pointed to by an IMG tag in your HTML.

update: shortened print command for clarity