Re: Photos are have grayed out
Sounds like those pictures have (partly) disappeared/been removed/deleted from your device, while their thumbnails have not (yet). If those picture files are not (complete) on your device anymore they can't be properly reproduced on the screen anymore, obviously.
Originally Posted by AC Question
If you have your device create frequent backups you can restore disappeared pictures. I auto-upload (a.k.a. 'sync', a.k.a. backup) every picture I take with/to Dropbox as soon as it was shot, so I always have backups without having to do anything for it. Added benefit: you can delete all pictures from your phone as soon as they have been auto-uploaded to your Dropbox and re-use all that storage space in your phone again and again!
Of course your Dropbox needs to have sufficient storage space available. Mine has 60 GB, enough for thousands and thousands of hi-res photos.