[WilliamDraco]

Yes as others have said - other people can see it, but only if they also have access to the same portrait.
This can mean portraits included in the Thay nwsync, or if multiple people have the same one from another source (as Bertram indicates).

So strictly to your question: "All the time" - likely not, but if you pick the right one, it could be at least most of the time :)