[TYPO3] How to modify a page header("Content-type:...)

[Bernez Johann]

Hi everyone!

I'm currently using an extension which works with mysql blob fields to store
pictures...

As you know, when you want to display one or more pictures, the page headers
should be define. In that case is must define something like that :
header("Content-type: $type"). Where $type is a mimetype image/gif or
image/jpeg.

My problem is the next : I can't modify header information in my class
because some content is displayed before this one, so I have errors like : *
Warning*: Cannot modify header information - headers already sent by...
And if I don't try to write header, just display one picture, it doesn't
work and I have something like : GIF89$^ù*$^à#@5343.... (strange char)

Is there a way in TS to declare header like this ? ( header("Content-type:
$type") )
Or an other method to display blob content without troubles ?

Thanks for your help.
Johann.