ok, here's the problem. you've got a bit of lint on your sensor. I've got it all over mine, dust in my case. The best way to avoid it, is to have pictures with a lot going on in the top right side of your shots. Another way is to stay away from an aperture of 6.3 or higher (stay around 1.8 or 3.5, if you use f/16 or whatnot, it'll have more depth of field, making the sensor a closer object of focus, hence the lint.) I'm assuming you know what aperture is since you have a decent camera. The reason it didnt pick it up in the last shot is because the light from the lamp wasn't your exposure bracket. if it were, the entire picture would be dark except the lamp, and therefore you'd see the lint.

if you've got a version of photoshop cs or higher, you can use the clone stamp tool to get rid of it, or search online for sensor cleaning swabs.

hope i've helped.