In Book 7, it's learned that one of the difficulties Snape has in getting the sword of Gryffindor to Harry is that Harry and Hermione are taking very great precautions to stay hidden, including keeping Phineas literally in the dark until Hermione slips when she says they're in the Forest of Dean while the bag with Phineas's portrait is open.
However, after the incident at Godric's Hollow, they gain a copy of Dumbledore's biography by Rita Skeeter, which has Dumbledore's portrait on the front cover. Hermione and Harry are often reading it; it's a window to them and the audience of Dumbledore's misdeeds in his early life, which is just one part of the general disillusionment inherent through the entire arc and definitely in Book 7.
If people in portraits can move between portraits of themselves, why couldn't Dumbledore have just camped out in his portrait in Harry's copy of the book? He could have gotten their whereabouts every day, maybe even where they'd be the next day, and he and Snape could have come up with any plan they wished to get the sword to Harry.
Is this just an oversight by Rowling, or is there some qualitative difference between a painted magical "portrait" and a printed magical "picture"?