regex and mime type help

[mydster]

I am a bit of a noobie... however, I've been reading the sitepoint php book and came across some code:

eregi('^image/p?jpeg(;.*)?$', $_FILES['uploaddedfile']['type']) )

Now, this basically checks the type of an upload file named 'uploadedfile'

My question is, what does this mean:

(;.*)?$ and why is ^ at the beginning necessary?

Thanks.

[Ghandi]

^ signifies the beginning. $ signifies the end.

(;.*)? i do not know.

for a decent tutorial.
http://www.sitepoint.com/article/974/2