The images showing the progress of a lunar eclipse were taken in increasing exposures to compensate for the decrease in brightness. The exposure increase from full moon to totality can reach 12EV or 4000× increase in light-gathering power.
Images showing the progress of a lunar eclipse appear in a constant brightness, and flat-Earthers —presumably never seen it in person— use it to “prove” a lunar eclipse is not caused by Earth’s shadow. In reality, the images were kept in a constant brightness by increasing the exposure of the camera.
The brightness of the Moon decreases during the progression of a lunar eclipse. It can be easily observed if we see it in person. It is very apparent, too. The Moon becomes noticeably darker as it progresses from a full moon to a total eclipse.
In a series of pictures showing the progression of a lunar eclipse, the moon appears to be in constant brightness as it progresses from full moon to total eclipse. The reason is that the camera is set up to compensate for the decrease in brightness by increasing the exposure. It is the reason the resulting pictures appear in similar brightness.
The difference of the correct camera exposures between a full moon and a total lunar eclipse can be as much as 19 stops. In other words, a full moon can emit as much as 500000× more light than during a total lunar eclipse.