This question highlights the need to look at preservation as a whole, and to tackle it with a multi-pronged system that mitigates and protects against a myriad of potential threats such as:
1. Hardware might become obsolete (Can the data be accessed in the future? Think of 8-track players, what if USB memory sticks are not usable in the future? What if the shape of the USB plug-in changes in the next ten years?)
2. Software might become obsolete (So your computer still works, but can your software actually open the file and sort the data into an organized manner that makes sense?)
3. Flood, fire, theft, rodents, etc.
4. Carrier might deteriorate or become damaged (oral histories on cassette tapes, data on CDs, DVDs, memory sticks, etc.)
5. To what degree can online content providers be trusted? Will they be operable indefinitely? What if they are bought by another company, go under, change their access policies?
I would therefore suggest that you consider developing a personal LOCKSS (Lots of Copies Keep Stuff Safe) system. This might look like the following:
Store a copy of your data in multiple locations in a variety of formats. Your working copy (the one you access and update every day) might be on your laptop or main computer. Write down the specs of your computer hardware and software - What version of Windows are you using? What version of Family Tree Maker, etc.? Keep the install discs and manuals for your software and hardware. Back up your files onto (at least one) disc, flash drive or external hard drive. Move this storage device outside of the home. By placing it in a safety deposit box or safe, you might be able to signal to your descendants that this was important to you. So that when they are sorting your effects, the genealogy doesn't just go into a miscellaneous pile. You could also include a note with it explaining that the information contained within is very important to you and that you would like it to be passed on to a family member who would take responsibility for it. They might also then get your install discs (computer even!), and access to any genealogical information you have stored online. Here, I would like to point you to the concept of a digital executor. Somehow, you should make access to your cloud storage or other online collections of your research available, should you pass on. As suggested by @Lennart Regebro, print out a hard copy of your research once a year or so. He suggests that this is a stable format that people will still be able to access (read) in the next 50 years, regardless of technology changes.
Ask yourself, are you trying to preserve the data information, or the format and way that it is laid out also? The two are not the same. If you want the data to appear as close to the way that your computer software makes it look to you right now, then you will need to build into your plan ways to keep the software readable, updated and transferrable over time. But if you are looking to preserve just the hard facts, then the printout @Lennart suggests will do the trick.
Some archives are attempting to build up stockpiles of obsolete or nearly obsolete hardware and software, so that they can access records stored on out of date devices, but this requires storage space to hold (potentially) rooms full of equipment, expertise to know how to use the equipment, spare parts to repair the equipment, time, budget funds, vision and foresight. When planning, you would need to think in the same manner... How would my descendants know what this is? How would they access the content? Do they need a password? Do they have the hardware and software to 'make it go'? Does it matter if the font is the same? The layout the same? Do the queries work?
All of this is to say that you need a plan, and that this plan should tackle all of the risks that you can imagine. Including human negligence or oversight. The shelf where you store things that are important to you might be obvious to you, but not to others. Label clearly and make copies; copies in different formats using new and old technologies. Lots Of Copies Keeps Stuff Safe.
ps - regarding your particular concern about photos - Following LOCKSS, your originals would be maintained as well as could be (acid-free folders, waterproof container, etc.) and copies would be made in a variety of formats... JPG, PDF, PDF/A, TIFF, (whatever makes sense for your system), etc. If there are negatives or slides then it would make sense to also keep or acquire the equipment needed to "read" them, like a slide projector.