You've obviously gotten a couple ways to do this, but I'll share mine, which is a little bit different. Primarily, I don't really spend too much time in photoshop this way. (Honestly? It takes about the same amount of time as it would take me in photoshop, it's just a different way of doing it)
first: How it looks in my game.
(Note: I personally hate having anything "intrusive" on top of the images, unless its a mouseover like in that screenshot. Instead if you notice the 3 lines to the top right? That is a drop-down objectives menu, which tells you everything you can do. I have a tutorial explaining it all beforehand.)
Now - as I said, I spent very little time in photoshop for this. Instead, I use daz. Specifically? Canvasses.
I just opened daz (no scene loaded, so there's a few things missing) for a screenshot, here:
By default canvases is not selected, and alpha isn't either - those both need to be checked off. Next step, is to select the objects you wish to render, and then goto the "Nodes" dropdown, and choose "From selected". It'll ask you to name the node, then it will appear in the node list. Select it from the node list, render and....
What it does, is it will render ONLY what you selected in the scene - so if you select a figure (and their clothes, and anything else you want as part of the button), it will ONLY render that, but it will still take into account all the other objects in the scene. What this means is shadows, lighting - even other objects in the way, will all be considered. But ultimately the only thing rendered is what you selected, and everything else is simply transparent. (Or black if you don't check the alpha box - that bit is important.)
Example from the above screenshots:
In this one I selected her, and the bottle, so that's what rendered. The table and everything else was accounted for, and still hid the parts of her that should be "hidden".
That image is my button - or more specifically, the idle button.
Adding an outline and lightness to that to create a hover image at that point is easy. Personally I just increase the lightness, add a stroke, and I'm done. You could do it any way you wish.
Here's an important note: I do not use imagemaps - so no hotspots or anything like that. I simply use full screen PNGs as the button (Idle and hover versions), and have them on top of the main render. By setting a focus_mask to the button, it ensures that ONLY the area that isn't transparent is clickable.
Another important note: Rendering a canvas in this way, takes almost as long as rendering the full image (Since it's still processing the full image, just rendering the majority of it transparent). For me this isn't a problem since #1 - render queues exist, and #2 - a render on average takes at MAXIMUM 20 minutes, usually well under, so the time it takes to render is about the same as I'd spend in photoshop messing around with layers and shit anyway, so I just find doing it like this a lot easier. Adjusting the lightness and adding an outline is trivial and takes a few seconds.
There's quite a few ways to accomplish this all, but that's mine anyway. I find it relatively painless and effective.
