When you take a digital picture the resolution you set within the camera determines the quality of the image.
Setting a high resolution takes up more memory and creates a bigger file, but the quality will also be better especially if at a later date you may wish to enlarge the image. The higher the original resolution the greater number of times you can increase the picture size and still retain clarity of the image.
Pixels are what make up a digital image, usually so tiny your eye cannot see them, however as a picture is enlarged the quality of the resolution will deteriorate and the picture will appear as little blurry squares, in fact what you are seeing is the digital pixels enlarged. (Pixelated !)
Most web sites require pictures to be of a maximum and/or minimum size to meet their publishing requirements. Your picture is too small so that when it is put in place it appears blurred and distorted.
If this is part of a Hub, when you uploaded the image you were given a choice of Full width, Half width or Quarter width, if you chose Full then reduce it to half and check to see if this cures the problem. If the picture is still pixelated at quarter width then you need a better quality original.
Hope this helps