To Select Additional Raster Images from the List
In the Raster Manager dialog, Ctrl + click the names of the additional images. That is, while holding down the Ctrl key, click the names of the additional images.
The additional raster filenames highlight in the Raster Manager dialog. If Display Raster Border ( , Raster Manager category's General tab ) drop-down is set to When Selected, the images highlight in the view(s) as well. If you Ctrl + click a previously selected image, it is deselected.