I came across this issue just a short while ago – a client had a header that they wanted to use on a WordPress website, but it didn’t fit the usual size constraints so when I added it the darn thing was shunted over to the left.  Not good!

So I found a nifty article that helped me sort it all out, just a quick and simple matter of updating some css in the child theme:

.header-image { margin-left: auto; margin-right: auto; display:block; }

Voila!