Stored on two fat RAID1 arrays in two different locations. Still also have some 30K slides (many scanned, but not all), and a bunch of 4x5 chromes. Have a few prints, but not too many.
I am a natural history museum curator, so cataloging is critical. I use a Filemaker relational database to catalog and annotate all my images including thumbnails. Images are sequentially numbered in series from 1 to currently 11,xxx; those are only the light optical images. I use NameMangler to change the default file names to my sequential series. Most of my shots are nature/natural history, so I catalog them by identification & classification plus location with GPS coordinates. Then there are some additional fields on gear used and some notes (filters, z-stacking, lighting, biological information). Natural history images are worthless without good data. There is also a hard-copy of the db information, just in case.
[I have not catalogued the SEM images that way, they are just in hierarchical directories from genus - species - museum-lot/collection-number; metadata are with the already captured specimen data. The ~13K SEM images from my last book are all on-line in an access-protected site; there are some copyright issues with specimen images, so I can't make it open-access. People can request access, but have to confirm personal use. Once I shuffled off, that access restriction can be removed: good luck suing me then!].
Some are on a stock-agency site, and royalties eventually go to a designated beneficiary. After retirement, I want to put a bunch on CalPhoto. This seems to be a good avenue for images that may be used for education, and still offers the option of contacting me (or later beneficiary) directly for any commercial application. This also eliminates the %$#&@@@ stock-agency and its rip-off.
The photo library is mentioned in my will with specific instruction on use.