The height of the image is fixed at 300px but the width is not fixed. It depends on your device screen width. the width for the image is 75% of your device width. for example if you use a devise which screen width is 1200px then the image width will be 900px.
and to remove the round image holder navigate to dokan/style.css on line 1516 and use display: none; like the following code to the class.