Imagine a scenario where Alice is homed on a Lync 2013 server, but has never signed in with the Lync 2013 client. Alice has an Exchange 2013 mailbox and she has loaded a high-resolution photo via Exchange 2013 OWA.
Will other users in the company, using the Lync 2013 client, see Alice's high-resolution photo in peer-to-peer and conference sessions?
No, they will not. The users will see the lower resolution version of the photo from Active Directory.
Why you might ask?
The reason is that Alice has not yet signed in with the Lync 2013 client. As soon as she does it, the Lync 2013 client will see that the high-resolution photo exists for her, and it will update the presence information for Alice to show that she has a high-resolution photo in Exchange 2013. When the other Lync 2013 users sees that presence information update, they will access and display the high-resolution photo for Alice.