Try using margin-top instead of animating the top property:
$('#latest-image-list').animate({marginTop: "-=20"}, "fast");
Here is a demo: http://jsfiddle.net/DTxQf/27/
In addition, on a side note, you created a height variable without a var statement that placed it in the global scope (otherwise it would be inside the scope of the window.load event handler). Always use var to make sure that you do not arbitrarily create global variables (which creates additional overhead every time you look at a variable).
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