Vanishing Photos

This weekend I spent most of my time putting photos back on the blog that I had accidentally deleted. Photos from the past few years were stored on a USB stick and any that were older I retrieved from my Flickr or Cut Out And Keep account. Very boring and time consuming. I went through the blog month by month making a note of the ones I'd corrected. When I'd finished some more photos had disappeared so I'm back to square one. I can't understand how they can just vanish. After doing a search I found that photos vanishing is quite a common problem and as yet I have not found a way to stop it.