On a master page anything you put in the head will be present for all content pages that use that master.
That is to say if in your master page you have:
<head runat="server">
<script type="text/javascript" src="/js/pages/jquery.min.js"></script>
<script type="text/javascript" src="/js/pages/jquery.jscrollpane.min.js"></script>
</head>
then every content page will contain the same thing in the head.
If you had scripts that were used by some pages and not others then on a master page you can define an <asp:content> tag that is in the <head> of the master page.
Then in your content pages you can place links to your javascript files right into the content place holder for the content tag in the page head.
If you wanted to link pictures, I would suggest doing this through javascript. If you created a <script> block in your master page head with something like the following:
var ReusableImageVariable = new Image();
ReusableImageVariable.src = '\A\Path\To\Your\image.jgp';
Then on any content page you could place a script block that would use that ReusableImageVariable and copy it onto the document in a specified place:
<script type='text/javascript'>
document.getElementById('PlaceHolderForImage').appendChild(ReusableImageVariable);
</script>
Where PlaceHolderforImage is the id of a <div> or other containing element. This would help with browser load times as well because you are loading the images the same time you are loading the style sheets and scripts.
Finally if you wanted to use just ASP, I would define the images as properties of the master page. Then any content page can just access them in code behind and load them where ever you need them.
