I categorize by camera and date and backup to external (detachable) USB drives as well as keeping a copy on a local drive.
I also keep a local "album" where all "favourite" images retain their original camera-generated prefix (personalised where possible to KP, K70, K3 etc.) and have a descriptive filename … eg K70_1234_grandpa.jpg
I can search the album for "grandpa", come up with an appropriate list, choose the image I want and recover a copy of the original in a few seconds.
In the event of potential duplication of file prefix, such as with the older IMGP-prefixed images, I'll use Irfanview (my default viewer) to check the EXIF to ascertain which camera was used.
Other shots taken at the same time will (obviously) then be immediately available.
My negative scans are similarly categorised, by format and/or monochrome or colour.
Mostly, on the odd occasion where I actually "need" to generate an image from an original, it's the work of moments to find it.
All very amateurish, very basic and very cheap, but it works for me and is totally non-reliant on any external web-based service (which have been known to "disappear" or become very expensive)