There's no way to centre an image that isn't a bit hackish, it's not functionality that is provided.

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If you really must, you *could* just precede the image by a load of `&nbsp;` - or wrap the image in `<pre>` tags and use normal spaces - to manually add spacing to give the *appearance* of the image being centred (see [this][1] MSO post for examples).

However, this might cause problems for viewers on mobile devices and maybe tablets (not tested, but I just have a suspicion...), so I'd actually advice against this - just leave the images where they are.

[1]: http://meta.stackexchange.com/questions/25835/is-it-possible-to-horizontally-center-an-image-in-sofu