Diligent owners seem to be a rarity. Per Graybyrd's comment the owners of the photos just shoved them in a shoebox that was then placed in a closet and apparently forgotten. If they hadn't been salvaged, they would probably be in the dump.
The flip-side is in other cases it makes it more likely the pictures will still be available to someone in 100 years. Whether or not they're related or even associate with/to the people in the pictures is another matter.
Before it was typical that photos would be taken, a few copies would be made, but the circle of distribution would be small. Now you can take a digital picture, and the circle of distribution goes from being only 2 to 4 copies in many cases, to potentially dozens of copies being made and widely dispersed.
This is even before we start looking at things like social media, and personal weblogs. Where for example, once you upload something to facebook, their TOS is such that even if you later delete the picture from your page, that doesn't mean they(Facebook) have to delete their copy of those same pictures. Likewise, there's nothing preventing other parties from vacuuming up those images should they have access in some form. Archive.org would be a big one known to many on this board in particular, as its often used to find older "lost" stories. It also grabs images a fair bit of the time.
Which isn't to mention what various governmental agencies and other largely unknown groups have likely picked up over the years and squirreled away in various datacenters.
As to future media compatibility, the only "iffy" scenarios are "early adopter" or proprietary media formats that never gained much traction. While Mpeg2 could be used as a counter-example to that already, as many consumer media devices on the market today can no longer natively handle that kind of encoding, which is the backbone of practically every Commercial DVD ever sold. There is no shortage of options available to re-encode that content to h.264 for use on the newer devices.
And given how common mpeg2 is, it is highly unlikely that utilities would be hard to come by in 100 years that could make such files viewable. Comparable story for gif's, png's, and jpg's as well. Some of the more esoteric picture formats are probably another matter however.