We didn't opt for it, but asked about it when we were on the Fantasy in December.
You can ask any of the shutters photographers about how to book it, it seemed that they had a good amount of availability when I asked.
The studio is in an enclosed studio at the corner of Deck 4 in the shutters area.
They said it was a private 20 minute session, not sure if you can have a longer session.
When pressed, they said the smallest package would be $500 but that there were different packages available. I didn't ask for any additional details about what was included in the package.
I would recommend taking advantage of the casual photo opportunities on non formal nights.
The lines are typically non existent and the photographers typically spend more time with you and your family and are more willing to retake pictures that don't come out right. One of
the photographers spent about 15 minutes with my family, going through different poses and groupings on the first night on the white background. Those were some of our favorite pictures from the whole cruise. Another night, we had my son and daughter dress up on a casual night and got some great pics against the Tinkerbell background.
The formal night was crazy and rushed.