Image kao content-Type header ?

Pošto sam novi u php-imam pitanje :

Kako bi u php-u napisao skriptu za izbor random datoteke (*.jpg) na jednom diru !
Ali to ne HTML kodom, vec direkt preko headera

Content-Type: image/jpeg
Content-Length: xxxx

slika

Nešto kao ovo :

http://www.starsphere.net/login/botcheck.aspx


znam za header :
("Content-Type: image/jpeg");

kako da dobijem Content-Length i saljem raw data ?

Za random isto znam : echo rand(1,xx)

kako da spojim to skupa i da stvar radi

probao sam i sa imagejpeg()
i dobio
supplied argument is not a valid Image resource in /home/xxxxx/public_html/test.php

pomoč molim :)

hvala unaprijed

Potpis

Pozdrav StratOS
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"It works better if you plug it in."
"As a rule, software systems do not work well until they have been used, and have failed repeatedly, in real applications."
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nešto najjednostavnije ti je

Evo ti konkretan primjer

Content-type: image/pjpeg
Content-Disposition: inline; filename=_filename_
Content-Length: _velichina fajla u bajtima_
Cache-Control: public; max-age=604800
Expires: 604800

To ti sve ide u header, nakon toga odshtampaj samu sliku/raw