Dynamic Images - header already sent?

I have made a dynamic image. This is the beginning of the code:

<?php

header("Content-type: image/png");

How can I add

<meta name="googlebot" content="noindex">

to the code in a way that would be sent along with that previous header information, but not produce a

Warning: Cannot modify header information - headers already sent by (output started at /home/********/public_html/imagez/sig.png:1) in /home/a7476356/public_html/imagez/sig.png on line 3```
error message?

Thanks!

Why would you want to include HTML in a PNG image?

You can't.

Just put that image in an /images/ folder, and disallow google to crawl the folder by making a robots.txt file.

system_meltdown wrote: You can't.

Just put that image in an /images/ folder, and disallow google to crawl the folder by making a robots.txt file. So there's no way to change the syntax or anything in order to give that?

I can't put it in a robots.txt file - I'm trying to include the file on another page on my other website, and see if Google indexes the page. It's all experimentation.