In several themes you can add a custom header image via Appearance > Custom Header (see this post). In iNove you can add an image to the right side of the header via Appearance > iNove Theme Options > “Banner”. Create a 60px high image, upload it via Media > Add New, copy its URL, and put it in the Banner box this way:
(For a less than 60px high image, increase the padding number accordingly.)
In Grid Focus you also get a small image at the right side of the header: your blavatar (uploaded in Settings > General).
Note: In iNove there’s a way to insert a header image across the entire header. But –like so many other things– it doesn’t work in Explorer, so I’m not posting it* (unfortunately more than 50% of internet users stick to Explorer, just because Microsoft has planted the thing in their computers)…
*Update: See here.
Update 2: for a Custom Design upgrade solution in iNove, see this staff suggestion.