View > Background Bitmap > Align
AlignBackgroundBitmap is the command
I still have a problem aligning bitmaps in rhino, always did. but what helps is to size your bitmaps equally so you can use the SNAP to grid setting to place them.
Example: you have two drawings, front and side:
neither are the same size.
Use a DRAW program (adobeIllustrator, Corel Craw or XARA) to alling them onto the same size image. This way, placing them in Rhino will be much easier.
In Xara you can make the image transparent so you can align them properly, exporting to two separate images.
(am requesting this thread be moved to the Modeller’s forum).