Unfortunately, Britney's autographs are signed by her assistant Felicia Culotta. It's been said over an over again that Britney sends secs on this forum, but I thought I'd just make a "master post" with the proof that has been found, so it's more convenient.
Vivalakayla sent directly to Fe via Vegas and got back this autograph:
http://surfmypictures.com/image/a325c71 ... 4yavn.html
The handwriting/personalization matches the personalizations on the "Britney" autographs.
https://www.startiger.com/showscan.php?scanid=597916
The K and a at the end are exactly the same. Fe is just a bit neater with her own mail.
There are ways to get an authentic Britney TTM, but it is very difficult and rare. One was via Planet Hollywood with an LOR (this was INCREDIBLY rare and most likely won't be your best shot) and the others were from contacting a person in Britney's team, I believe. There have been a few Femme Fatale signed promo photos and 5x7 promos that were given out.
https://instagram.com/p/zdLphImJmu/ &
https://instagram.com/p/y6YnjLJyUn/
Regarding other celebrities dancingirl1 named:
Taylor Swift use to sign TTM and VV back when she wasn't HUGE around 2006-2010. After that she stopped signing, but many people did get her from private emails. I believe that most, if not all, of the emails are spammed now. However, there is currently a working private address.
I don't think Beyonce has ever signed TTM or VV, but she does have a working private contact.
These celebs do not require you to know someone within their teams, but they do require a lot of research and work to find private contacts that work.
I have never seen successes from Mariah, Janet, and Madonna. I believe that these do require knowing a team member, getting them IP, or paying for a meet and greet.
BTW to dancingirl1: I would love to see the autograph you got from Britney via a member of her team.
EDIT: One of my links is to a scan on star-tiger but it doesn't seem to work since ST is changed to google for some reason.