Images Must Be Sent In High Resolution
When you send images to your web designer, make sure they are high resolution. If they are too small in resolution, they are impossible to work with in terms of fitting in a certain area.
Let's say a designer is sent a photo with the dimensions of 200px height and 200px wide, and it needs to fit into an area of 1920px by 600px. Obviously, the image that was sent will be to small to fit within that area, creating pixelation.