code: public Observable<ImageInner> getByResourceGroupAsync(String resourceGroupName, String imageName, String expand) {
          return getByResourceGroupWithServiceResponseAsync(resourceGroupName, imageName, expand).map(new Func1<ServiceResponse<ImageInner>, ImageInner>() {
              @Override
              public ImageInner call(ServiceResponse<ImageInner> response) {
                  return response.body();
              }
          });
      }
docs: Gets an image.
  
  @param resourceGroupName The name of the resource group.
  @param imageName The name of the image.
  @param expand The expand expression to apply on the operation.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the ImageInner object