edit: assuming keynotes accepts PS EPS
if you want to remove the background leaving just the image, you have to create something called a clipping path.
there are a number of ways to create the initial path, the easiest in this case would be to select the magic wand select the background, this will give you a selection around the object then you must inverse the selection (CMD+Shift+i)
Then go to paths (found in the layers palette) in the top right corner is an arrow for a submenu, go there and "make work path" a new path will appear, double click on it and name it what ever you like.
a line (vectored) should now have appeared around your object in the main window, still in the paths palette, again go to the arrow in the top right, and select clipping path, and small window will appear with a drop down, select the path you created earlier, and leave flatness alone...i dont think in this instance it will make any difference.
the clipping path has now been created BUT you have to save it in the correct format, so go to file and save as a Photoshop EPS (NOT DCS EPS)
job done 🙂...at least that should work, i typed this out without actually doing it but im confident its correct...if not im sure someone will correct me.
also just as a pointer when you have saved as an eps, a small eps options window appears, you can if you wanted select a compression (to make the file smaller) its under encoding you can select Jpeg maximum quality.
Hugh