[Charlie8776]

Wow, this is getting rather complicated. Thank you for your help. I'd like to keep things simple, where possible. I'm trying to get around the ElementByID restrictions with the code below, but it doesn't work:

function plus() {
	document.getElementsByTagName('img').width += 200;
}

function minus() {
	document.getElementsByTagName('img').width -= 200;
}

<a href="javascript:plus();">+</a>
<a href="javascript:minus();">-</a>

<img src="index/img/1.png" class="testclass">

.testclass {
	border-bottom: 1px solid #BCBCBC;
	border-right: 1px solid #BCBCBC;
	border-left: 1px solid #EAEAEA;
	border-top: 1px solid #EAEAEA;
	margin-bottom: 25px;
	width: 60%;
}