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The Apple TV displays photos from your iPhoto albums in chronological order. If for whatever reason you wish your albums to display in another order, drag the photos into the order you require in the album in iPhoto, select all the photos in that album and change the date using batch change from the photo menu.
Thanks for your prompt answer. As best as I can tell, the photos are displayed in the Album in chronological order. This particular Album is made up of all family photos taken at Easter over the years. I've pulled the photos from other annual Albums. If I "batch change" the date on the photos in the Easter Album, it will also change the date on the annual Album photos which will get them out of order there. But, again, as best as I can tell using the Info displayed for each photo, the Easter Album is ordered chronologically.
Most of these photos were originally slides which have been digitized by scanning and importing into iPhoto. I have then painstakingly "batch changed" all those slides to give them the correct date for when taken rather than when scanned or imported.