As per @Olivier's comment, if it's a brand new camera as you say, and you can't see anything on the outside of the lens, and it is doing a similar thing on every image, check the very first image file, 0001, if you downloaded and still have that, then it's almost certainly on the inside of the camera.

The Canon powershot SX700 doesn't have a removable lens, so don't attempt to get inside it, as this will invalidate the warranty.

I would suggest that you contact the place you bought it from in the first instance: if it was from a shop, take it back into the shop. Take with you a sample of the first or earliest image if you can, and also the receipt. If you bought it online, you may need to contact them via an online account to arrange a return before you post it back to them.

Depending on what country you're in, the contract is between you and the shop/online seller that you bought it from (the exchange of money and goods), therefore they would usually be your first point of call for any issues. Failing that, you should be able to register with Canon for support, by entering the serial number and purchase date.