Why are the photos taken by the spaceship so unclear? Isn't the pixel of space camera not as high as that of civilian?

No, the camera resolution of the spacecraft is very high, and it is very difficult to shoot because the celestial body is far away from the satellite.

The earliest blue marbles on the WeChat startup screen are the earth shot from space 45,000 kilometers away, which is very clear:

Now the startup screen is changed to the Earth shot by China Fengyun IV.