ACP -> Look & Feel -> Your Skin -> CSS -> ipb_styles.css. Ctrl + F and search for ".ipsUserPhoto" It'll look something like this I believe:
.ipsUserPhoto {
padding: blahblahblah;
background: blahblahblah;
border: blahblahblah;
box-shadow: blahblahblah;
}
Remove the line that start with "border" and it should fix it.
I like the look of Mac OS, but I like the price of a windows computer more. I don't have the budget to lay down ~1k for a computer. I'm as of writing this still on 8.1 and will most likely not upgrade.