The difference would be that the user's web browser is going to pull the image file from a different server. Their computer may need to hit DNS for that second server, which could slow things down (albeit pretty much imperceptibly, and only for the first such image).
It really depends on the speed of either server. Things will go faster from whichever server has a better network connection and less latency.
Plus, if both connections are roughly the same, it's pretty much impossible to know which will be faster, as it'll be different for different people in different locations.
- Jeff @ DreamHost
- DH Discussion Forum Admin