To Select Additional Images in a View

Select the Raster Selection tool (Drawing > Attach > Raster > More split button).
<Ctrl + click> the additional images. That is, while holding down the <Ctrl> key, click the additional images.

The additional raster filenames highlight in the Raster Manager dialog (if open). If Display Raster Border ( File > Settings > User > Preferences , Raster Manager category's General tab ) drop-down is set to When Selected, the images highlight in the view(s) as well. If you control-click a previously selected image, it is deselected.