In Didger 3, you cannot change the projection of a bitmap imported into a vector project. The View | Change Projection menu will be changed to View | Projection Settings. To change the projection of your bitmap, import it into a raster project, specifying the georeference information. Once the bitmap is imported, go to Image | Convert Image Projection to convert the image projection to that of the vector file. Once the projection is converted, export it again as a GeoTIFF.
Didger 4 and Didger 5 solve this problem as there is only one project type.
Updated March 20, 2014