When answer questions like this, it is important to think about what you are visualizing while reading the text. This should help with your explanation. To reinforce means to "back up or prove" with evidence. For example, how would a picture of the Dr. Martin Luther King, Jr. exhibit in Washington D.C. reinforce the speech he gave? The picture proves that the speech as well as Dr. King himself were a powerful presence to all. He was so important to the change of Civil Rights in our country that the monument is a testament to that change.
The text uses descriptive details to help the reader understand how a chronometer works, and the image reinforces those details. The image allows readers to see all of the individual parts of the chronometer, such as the dials and the wooden case. It might be difficult for the reader to visualize how the chronometer is suspended in a swiveling brass ring, but the image helps the reader understand exactly how the chronometer is put together.
