If you can deal with having a text box placed on your page (perhaps with absolute positioning property if you need, no line - no fill for an invisible box, and no internal margins; you might have text wrapping issues outside the box, as well, that you'll need to deal with manually), you can insert the picture inside the text box and put a shadow on the text box instead. You may need to resize the picture to somewhat once inserted, but if it's really larger (or really smaller) than the text box, you might want to consider resizing the picture first in an image editor (save as a second image, perhaps, leaving the original alone). Also, if you use this method, consider setting the text box to center horizontally and vertically (or left and top) before inserting the picture (use the Table menu, treating the text box as though it were a table cell).
