lomapaseo,
It's not a processed image, but side-scan sonar images are difficult to interpret and often require expert knowledge
My guess is that the sonar fish was moving parallel to and near the right side of the image. Bright areas indicate objects that reflect an significant amount of energy back to the fish and are therefore sticking up above the sea floor. Behind the bright areas, you typically see dark areas that are shadowed from the beam. Note the shadow to the left of the box, behind the "object".
See here for more details:
https://en.wikipedia.org/wiki/Side-scan_sonar