Making an image service layer transparent

Steps:

1. Add two image services in ArcMap.
2. Arrange the image services layer so that the layer with the NoData region is on top. The NoData region in the topmost image service is marked by a particular color defined as the background color on the Service Properties dialog box.
3. Right-click the top image service layer in the table of contents and click Properties.
4. Click the Display tab.
5. Check the Make service background color transparent check box.

   This option renders the NoData regions with the service background color transparently so that you can view the underlying image service layer.

6. Click OK to close the dialog box.