In my experience that's never something you want to be asking yourself! Yes, it's true, absolutely anything you ever think of or do could be done be someone else. But, will they do it with as much care, attention to detail, tenacity, user empathy, pragmatism, and efficiency as you? No, of course they won't!!! If you believe otherwise, you will never be able to release anything, or if you do, and someone else comes along to compete with you (which always will happen if you're successful), you'll give up.
If anything, the opposite is true - building something extremely complex and beyond the current research cutting edge is something that big companies are more likely to be good at. Or if you do it, and they see it can be done, they'll be more likely to be better at catching up and passing you.
Smaller companies are great when they pick something they care about, and is within their capabilities to do a great job of. Dropbox is a great example - pretty much every big company had already tried to do file sync (Microsoft had tried at least 3 times!) but Dropbox did it with more care and pragmatism.
When I started FastMail, pretty much everyone told me that it was pointless to compete with Yahoo and Hotmail. But I went ahead anyway because I felt like what I wanted to create was something that no-one else at that time had yet created, and I wanted it to exist (that is, synchronized email across all your computers).
So, once you become the first person to build a great (for example) super-res product, you are now the leader, and can move on to adding lots of other great features for cleaning up old photos and scans. Everyone else is now playing catchup. And of course they've all got their own priorities, which are keeping them busy!
Anyways, as I'm sure you can see, this is something I feel very very strongly about. We have to believe in ourselves, and we have to build things that we want to see exist, and can't be assuming that someone else is going to do it better than us!