I dont think any positive ID can be had from that picture. It doesnt show the coralites very well and is at a bad angle. On top of that the specimen is to small to show real growth patten.
Alls you can probably say is Acropora sp. It does have polyps and a base simaler to M. Digitata but doesnt have that apperence towards the top from what I can tell.
Acropora sp. will be as good as it gets with that picture. Just about impossible to ID an acro to species level with a picture. Nothing about it stands out.
And I do agree w/ Reefland. You cannot identify an acro accurately at all down to species level w/o detailed skeletal analyses as well as knowing where the coral was pulled from the ocean.
sp. is a shorthand way of writing species when you aren't sure what the actual species is. So this unidentified acro would be classified as an acropora sp. unless Charlie Veron stops by and figures out what it is.
Is it a fresh captive grown frag? If so, ID-ing may be impossible.