[bes]

в простейшем случае это может выглядеть так

<style>
img {
	height: 100px;
}
</style>

<a href="#">car</a><br/>
<a href="#">animals</a>
<div class="content"></div>
<script>
document.addEventListener("DOMContentLoaded", function(e) {
	var content = document.getElementsByClassName("content")[0];
	var links = document.getElementsByTagName("a");
	for (var i = 0, length = links.length; i < length; i++) {
		links[i].addEventListener("click", function () {
			var xhr = new XMLHttpRequest();
			params = "test=" + encodeURIComponent(this.innerHTML);
			xhr.open('POST', 'some.php', true);
			xhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
			xhr.send(params);
			xhr.onreadystatechange = function() {
				if (xhr.readyState == xhr.DONE) {
					if(xhr.status == 200) {
						content.innerHTML = xhr.responseText;
					}
				}
			}
		});
	}
});
</script>

some.php

function images($dir) {
	$files = array_diff(scandir($dir), array(".", ".."));
	foreach($files as $value) {
		$path = $dir."/".$value;
		if (/*!is_dir($path) &&*/ pathinfo($path)["extension"] == "jpg") {
			echo "<img src='".$path."'/>";
		}
	}
}
if (!empty($_POST["test"])) images($_POST["test"]);