User blog comment:Person1507/Phineas and Ferb The Movie: Across the 2nd Dimension Ending/@comment-961279-20120514045133

If you do a search on YouTube, you can find the video of Dan talking with people at ComicCon 2011 after the movie was shown as a special preview. That section where Perry looks at the pictures was a last-minute addition because Dan suddently realized that Perry would be the only one who would remember this.