Header image alt text

I was wondering if there's a way to change the alt text of the header of my forum to the thread title?

Thanks

The alt text is used to describe the IMAGE, not the context of the page it's on. Changing it to anything but describing the image is non-semantic, creates accessibility issues, and is otherwise not recommended.

Sorry if I didn't make it clear, I meant the header image

My experience has always been it improves seo results.

Thanks