You have to select some station points in the image so that QTopo knows how to insert it as background. Two stations are the minimum requirement. To select a station click on it on the image: it will be maked by a cross and a dialog will ask you the station name. Type it in and click the "OK" button: now the station name appears near the cross.
When you are done click the "OK" command button. The image will be imported as background sketch in the drawing window. Be aware that the background sketch is not saved with the drawing. Therefore you lose it when you close the drawing window.