you could set up an if statement to check the variable gallery_page and display text base off of that, or if each page is for a specific chapter i.e. page 1 is chapter 1, page 2 is chapter 2; then
$ chap = gallery_page + 1
label "Chapter [chap]"
keep in mind gallery_page is 0 through (however many pages you have) and you must have 6 images only for the chapter .