They call them 'appear and waive', which is a stupid name. Character sightings or something would be better.
Mickey and Minnie greeting you on board replaces the Sail Away party.
I would suggest watching the videos of Adam Hattan's staycation cruise. The friend he cruises with, Gary C, loves characters and half their time was spend meeting characters. They talked beignets with Tiana, joked with Goofy about eating at Palo, it happened several times during the cruise that they run into Donald (Gary's favourite), while Gary is wearing a Mickey t-shirt. Which almost turned into a running gag.
A picture rarily shows good interaction, especially when it's a standard posed picture. With a posed picture, you never know what happened before or after. Better look for videos.