As mentioned. haze, humidity and even a spec of dust inside the lens. But I feel it's more of a smudge on one of the lenses. I suspect the cloth you're using to clean the lens may not be the one best suit for it. One might even say the smudge is on the outer lens when it could be on the inner lens. Best check and clean both sides of the lens with a microfiber towel and if you have a carry case, best use desiccant packs to draw out any moisture.
Here's a sample of lens flare which is what is your problem
Look to the right side of the sun. The two spots of flare are similar to ones in the original posters question. That doesn't make it a bad image, just something that happens occasionally.
Look to the right side of the sun. It isn't a problem in my mind, but it is a flare mark like the original poster had in his image.
I had similar "haze" in a few of my photos .. I traced mine to I touched the sensor some house and it was a light finger print that moisture seemed to react to it from time to time.
Also make sure your lens glass is cleaned on Both Ends.
You can buy a sensor cleaner kit and it will do wonders.
I suggest you search YouTube. With your camera MFG on how to clean your sensor, so you do it correctly.
But it was really easy and fast .
If you want to reply, then
register here. Registration is free and your account is created instantly, so you can post right away.