Importing Images:
The easiest way to import a file into an existing image is to drag its icon from the Finder into the canvas of an existing image in Opacity. This will import the image into the current layer. You can achieve the same thing by selecting the Image > Insert File menu item and selecting the image you want.
For both approaches, the supported file formats (in addition to Opacity's supported formats) are the following:
PostScript image
JPEG 2000 image
Adobe Photoshop document
Adobe Illustrator document
X bitmap image
Microsoft Cursor
TGA image
Silicon Graphics image (SGI image)
QuickTime image
FlashPix image
MacPaint image
OpenEXR image
Radiance image
Many common image formats can also be imported by choosing Open and selecting the image file.