Q: why are my photos disappearing in iphoto?

Greetings gavinfromjohannesburg,

Thanks for using the Apple Support Communities!

I understand that it seems you may be missing some photos based on the picture you provided. It appears as though you are using the new Photos application, not the older iPhoto application as your title suggests. 

If this is the case, I would recommend repairing your library using the steps located in the following article. 

Photos for OS X: Repair your library

If you; however, are using iPhoto, the steps to rebuild that library can be found in the next article. 

iPhoto 6 and later: Rebuilding the iPhoto library - Apple Support

Have a great day!