Hoarding is, from what I've seen personally, a deep-seated irrational fear of getting rid of things, even absolute junk in bad condition--it almost seems to cause physical pain when you suggest or try to make a hoarder throw something away.
I had a next door neighbour who was a hoarder. He was Hungarian and had been a prisoner in a labour camp during World War II. For him I suppose, possessions were security, and power, and having control of his life, which he had not had in the camp. He was not as bad as some people you see on the TV programmes about hoarders. Stuff wasn't piled up to the ceilings, he could for example walk upstairs, his bathroom and toilet were clutter free, but his bedrooms were full of stuff, his loft, his shed, and the garden had lots of furniture under tarpaulins. Wehn he died it all got thrown away,save for some stuff that went back to his family in Hungary, and a cup and saucer and a bowl which my Mum and I chose as mementos.
The only trouble with givng away clothes is that sometimes I do it, and then find that I want womething, and I haven't got it. I did this with a corduroy overshirt recently, and it would have been just nice to wear on a day that was not freezing, but not cold enough for a woolly cardigan.
As for family photos, scan them by all means, but make very sure that no one else in the family would like the originals. My SIL is still spitting blood about her aunt who got rid of all the family photos without asking if anyone was interested. And she did not scan them first, so no copies are available at all.