I tried the iframe script you suggested. Still no image. Where there used to be a little square where the image should have been, there was a white-outlined rectangle with no image.

Is it possible that my PHP installation got corrupted and is messing everything up?

Did you look at this?

Yes. As I said, I tried <iframe><src="headerpics/abb-heading-1d.jpg"></iframe> and the image did not display.

Once upon a time there was a man who was trying to find a picture. He knew which storage building he kept the picture in but he couldn't find the right 'PATH' to the storage building.

Stephen,

I'm pretty sure Eric was giving you a hint when he said:

"I would take a close look at this.
<iframe><src="headerpics/abb-heading-1d.jpg"></iframe>"

Stephen,

As the guys have hinted, the info you've presented does suggest that (somehow) your browser no longer finds that .png file.

It's all too easy when trying a new idea (such as using PHP's require() or include() functions for the first time) to accidentally break something that previously worked.

Debugging suggestion: Use your browser to examine the HTML source code that WAMP is handing to it. (Exactly how to do that depends upon which browser you are using.) Find the line in the HTML code that points to the page's header image. Compare the path shown there to the path in the page's older, pre-PHP version that worked as desired. Do the paths shown in both versions point to the same file location?

Your html has errors

which is why everyone is telling you to check your html code.

Eric was not suggesting you should try this, he was pointing out your error
In the post where you pasted the PHP code you will find the above code, change it to <img src="headerpics/abb-heading-1d.jpg" />