<%= image_tag('Lab_Potion.png', :style => "z-index:19; position: relative; float: right;") %>
will work. get rid of the space in the file name too, if not just for my sanity.
The random numbers are like a security feature and on each precompile the numbers end up changing. It's more complicated than that, but that is the gist.
And lastly, i doubt you have a img
folder as well.