If you have more than 1 photo and it is aligned to the center it looks a little weird but here's what you can try,

[gist]
body #es .es-photos.pattern-tile.photos-1 .es-photo a.fit-small b,
body #es .es-photos.pattern-tile.photos-1 .es-photo a.fit-width b,
body #es .es-photos.pattern-tile.photos-1 .es-photo a.fit-height b,
body #es .es-photos.pattern-tile.photos-1 .es-photo a.fit-both b {
text-align: center;
}
[/gist]

I put it in my custom css, it seems to work.
thank you very much

You are most welcome

Do you have a solution for es mobile?

It will work on mobile too. Perhaps your browser is caching the css?

thanks a lot Mark

No problem