I have a Nikon D40. I bought it new in 2007ish and I'm still using the stock 18-55 lens that came with it.
In the last month I've noticed a black fuzzy spot in every picture. Below is an example. That is not something on the wall - the dot moves and shows up in other pictures.
It only shows up when zoomed in and gets progressively lighter as I zoom out.
So I assumed it was something on the lens, but cleaning it didn't change anything. I don't visually see any scratch or debris. I don't think I ever took the lens off since 2007, but I removed and gently blew some compressed air into it. No change.
Any other ideas? The camera has never been dropped or damaged.
One other odd thing is that periodically, I'll see an extreme blue tint if I pick the camera up after a long period of time and snap some pictures - that has only happened once or twice in the last couple of years though and could easily be a low battery or temperature issue (I haven't really documented it).