[mceachen]

> which of two identically sized and timestamped files is the least corrupt image

What I've found on my older hard drive backups was file corruption due to bitrot or file truncation.

I use `jpegtran` to validate JPEG bytestreams, `dcraw` to validate RAW images, and ``ffmpeg` to validate videos. At least for my quarter-million-file corpus, those tools detect corruption sufficient enough for me to want to skip the file. I actually had to write a bit rotter to write tests for this, and do glitch inspection.

> To offer "principle of least loss" for mass merge of diverse collections, this would have to be figured out

Every unique SHA gets copied into your library (if you have copies enabled), but any given asset will have 1 or more asset files (that are merged in the UI and DB). To minimize risk from bugs^H^H^H^H "undiscovered features," PhotoStructure never moves or deletes files excluding it's own cache and db.