Do I need a different-sized image for each of the ImageWells I see in the Inspector area for App Icon? It seems that I can just drag the same icon, say MyIcon_32 into each of those ImageWells and it expands or shrinks as needed.
If you did not hire an icon designer then yes, it works that way. Start with your largest icon and you can drag from the larger cells downward.
If you hired a professional designer they will re-draw your icon at each size so it looks beautiful and proper at each size. They will provide you with an image for each size, and usually make the .icns for you. If they provided the .icns for you I would recommend using a copy files step or AppWrapper to replace the icon with the one your designer provided.
I really, really, really recommend hiring an icon designer.
I have downloaded them from iconfinder.com, and can get the various sizes as needed, separately, without a problem. I just thought maybe I didn’t need to download all 3 or 4 sizes after I noticed “one will do.” But I understand what you’re saying and will continue grabbing one for each size and drag it in that way.
They provide ICNs as well, but I’ve been using PNG files and dragging them into the App Icon ImageWells. I’ll have to read up on ICNs. Never used them before.