If you have built a site package from sitepackagebuilder.com and you are noticing that there are no arrows in the lightbox generated from the images content element, or from the carousel content elements, you are most likely missing the PhotoSwipe directory under typo3conf/ext/<yourextension>/Resources/Public/Images

These are available in the bootstrap package under typo3conf/ext/bootstrap_package/Resources/Public/Images. Simply copy the photoswipe directory accross to your sitepackage, and magically the icons will appear again (after refreshing the cache)

Strictly speaking you only need default-skin.png, but the pre-loader.gif animation for load waiting is also used, and will throw errors in your logs if it is missing.