Q I am running iPhoto 9.4.3 under OS X 10.8.5, and have not printed directly from iPhoto for some time. The other day I went to do so, only to be told that the Theme was missing. Where does iPhoto keep Themes, and how can I work around this?
A Normally current iPhoto themes are stored inside the iPhoto app itself, in the path iPhoto.app/Contents/Resources/Themes.
Some localised components are tucked away in the Themes.Common folder inside the Resources folder there. Additional themes, including those converted from previous versions, appear in /Library/Application Support/iPhoto/Themes.
You might be able to keep themes in folders having a similar path in other libraries, including that in your Home folder, but those do not appear to be usual. When themes are correctly located, iPhoto should find and use them automatically, and there are no user controls available.
It is worth Repairing Permissions to ensure that this is not the result of incorrect permissions. However you probably used a legacy theme which has not ported across to an update, or has somehow become lost. If iPhoto cannot handle an old theme properly, change theme via the button at the top right of the window.
Comments Photos keeps its Themes in the path /Library/Application Support/Apple/Photos/Print Products/Themes. Currently there seems considerable overlap with iPhotos Themes, but when you switch to Photos you may find yourself having to change themes to adapt. Apple has not yet provided any advice as to whether Photos can use old iPhoto Themes, but that appears unlikely.
Updated from the original, which was first published in MacUser volume 30 issue 01, 2014.