trick summary:

enter in you jpeg comment field: "<html>...your page...</html><!--"

then the "image" will look like:

   @^PJFIF^@^A^A^A^A,^A,^@^@000^Cr<html>...your page...</html><!-- rest of garbage

to the browser this is just the same as:

   \n
   \n
   \n
   <html>...your page...</html>