Modeling - Once you add a raster image, it will be displayed under 'Images' folder in the part navigator.
Drafting - After adding first image, if you start 'Image' command, then the respective dialog will show the 'Images in Part' to left side of the dialog.
You should be able to add multiple raster images.
Are you trying to add the same image, or specifying a new image? The only time I saw the initial image disappear was when I browsed to select the same image to place on a new plane rather than select the images from the Images in Part selection field.
The raster image are not a part of the history tree.
You will see a group of the raster images above the tree.
if you expand this group you will see all the pictures that are in your part. only if you add the same picture for the second time then it only will show 1 time in the raster image group.