53 GB in iLifeAssetManagement folder but only 5 GB in Photo Stream

I've got a 128 GB 11″ MacBook Air running Yosemite which I use for travelling and managing photos while on the move. With only 128 GB I try to manage the disk space carefully. But now I find there is only 10 GB left. About This Mac → Storage shows that photos take up 61 GB of this.

Drilling down 52.7 GB of this is in the folder ~/Library/Application\ Support/iLifeAssetManagement/assets/sub which I understood to be Photo Stream. It shows in a very large number of folders, each containing a single jpg file.

But if I pull out the images by using the Finder window searching for "image" and then selecting from kind "image" (I understand the standard way to pull out Photo Stream) the resultant file is only 5 GB large

• Why is this folder showing nearly 53 GB when Photo Stream is only 5 GB?
• What constitutes the other 58 GB?
• How can I identify them and delete those I don't need to free up some much-needed disk space?

The sub folder contains all the legacy photos from iCloud and iPhoto and normally should have photos and videos.

With 10.10 and the new Photos app, everything appears to be stored in ~/Library/Containers/com.apple.cloudphotosd/ and not in Application Support once you open the new Photos app and allow it to migrate things.

If you're in that situation (open the Photos app once and letting it set up a library and choosing which Photos to store locally), you should be able to confirm that nothing in iLifeAssetManagement is needed anymore and safely delete it after making a backup offline just in case we don't know all the tricks Apple has pulled.

Be sure to open iPhoto one last time and see if you need any of the photos there. If not, consider deleting that app and then converting all the iPhoto albums into Photos app albums and deleting the iPhoto Libraries once you have also an archival copy of these Libraries for "just in case" needs stored offline.