Here is a suggestion, but you would have to be able to write a plugin.
You need syntax plugin which outputs some html and javascript:
1. an html drop-down menu ( i.e. Selection element), where the options are the images you want to select.
2. an image element where the javascript can load the changed images
3. a javascript function which is called by the Selection menu and changes the images in the image element.
Now you might want to write a separate image plugin which will be able to place the image html syntax on the page, where you want it to be placed.
So here are the basics which the plugin has to output:
<img id="change_this_src" src="default.png">
<form>
<Select onchange="change_image()" id='my_images'>
<option value="path_to_image_dir/img_1.png>Image One
<option value="path_to_image_dir/img_2.png>Image Two
<etcetera. . . .>
<select>
</form>
Then create a file called script.js with this content:
function change_image() {
var select = document.getElementById('my_images');
var selection = select.selectedIndex;
var img = select.options[selection].value;
src = img;
}
Place script.js in your plugin directory.
Check out the dokuwiki plugin documentation:
http://www.dokuwiki.org/devel:plugins