Although you cannot use the align command on inserted images, you can move them with precision using object snaps: endpoint, for the corners and midpoint for the middle point of each side of the image. Of course this refers only to the border of the image, there is no way to align pixels using object snaps.
Keep in mind that if you insert a image directly on your sheet the image should be placed inside your titleblock border because if a part of the image extends beyond the title block then Revit will use the image as the titleblock's extend when printing. if you want to have an image that expands further than the titleblock's border without affecting the printing result you should insert the image in a drafting view and then place the view on the sheet.
Images and Drafting views cannot be cropped.
So, in général it is better to import images that are already cropped and framed to fit your layout.
hope it helps
aghis