how to send png image from server to display in browser via ajax

You could display a default "no access" image to users who are forbidden to access the image:

<?php$file = $_GET['file']; // don't forget to sanitize this!header('Content-type: image/png');if (user_is_allowed_to_access($file)) {    readfile($file);}else {    readfile('some/default/file.png');}

And, on the client side:

<img src="script.php?file=path/to/file.png" />

Alternatively, if you really really want or need to send the data via Ajax, you can Base64 encode it:

<?phpecho base64_encode(file_get_contents($file));

And place the response in an img tag using the Data URI scheme

var img = '<img src="data:image/png;base64,'+ server_reponse +'"/>';

Given that the Base64 encoded data is significantly larger than the original, you could send the raw data and encode it in the browser using a library.

Does that make sense to you?

Instead of getting get_image.php through AJAX, why not just use:

<img src="get_image.php" />

It's practically the same thing. You can just use AJAX to update the <img> dynamically.

You can't do it via ajax.

You could do something like this:

<img src="script.php?image=image_name" />

Then use JavaScript to change the query string.