If the image still has a smudged spot, you may need to clean the sensor. If you are not comfortable with doing this, please contact a professional for help.
If you want to try it yourself, you can use the following steps – but remember to be patient and careful.
To test whether you have any sensor dust, take some pictures of a blank wall or blue skies with the smallest aperture. Then look at the images on your computer (preferably in Photoshop) to see if there are any “dark spots.”
1. Try the camera’s auto cleaning.Many DSLR cameras come with an auto clean mode. Before you turn on the auto cleaning, make sure that your camera battery is fully charged, because if it turns off in the middle of a cleaning job it may damage the sensor or shutter.
2. Dry Cleaning.Just like we already did to the lens above, dry cleaning is step one to get rid of any tiny particles on the sensor. Again, make sure the camera battery fully charged.
To access the sensor, you can usually find the “cleaning mode” listed under settings as “sensor cleaning” or “mirror lock.” When you turn it on, you can hear a flip sound and see the sensor exposed.
Use one hand to point the camera vertical or downward to avoid getting more dust on the sensor and use the other hand to hold the air blower and gently puff a few air bursts.
3. Wet Cleaning.If you have to proceed to this step, make sure you purchase a specialized sensor cleaning kit and refer to the information on the manufacturer’s website about proper sensor cleaning.