If you wanted to create a dynamic img
element with a variable as the link or part of it you could do:
//These are just example variables, you can use your own the same way.
var imgPath = '/images/blog/';
var size = '200x450';
document.createElement('img').src = imgPath + 'yourImage' + size + '.png';
For your example i would suggest creating an array of links that you can access using a random number, for example:
var links = ['restOfLink.gif', 'anotherexample.png', 'yetanother.jpg'];
To select a particular image from inside the links array
you need to pass it the index it occurs at, with 0
being the first.
So for example:
links[0] --> "restOfLink.gif"
links[1] --> "anotherexample.png"
links[2] --> "yetanother.jpg"
See this JsFiddle demo using this method.