You are saving the downloaded image from a bitmap, it means you are reencoding it, because of that the images are different.
If you want they to be equal, then save the original array without processing.
Also, to compare image bytes already encoded is not a good idea if what you want is to compare the pixel data and not the encoded data (a png and a bitmap can represent exactly the same image but the encoded array will be completely different)
If you want to compare pixel data, then you can load both bitmaps, use LockBits and then compare the pixel data.