Revit Architecture
Revit Structure
Revit MEP
(Decal Types). 
Link panel
Decals drop-down
(Decal Types) 
Manage Project panel
(Decal Types) 
Link panel
Decals drop-down
(Decal Types)
(Create new decal). The Decal Types dialog displays the new decal name and its attributes.
Click
(Browse) to navigate to the file. Revit supports image files of the following types: BMP, JPG, JPEG, and PNG. See Best Practice for Storing Image Files.
See Decal Attributes.

Now you can place instances of the decal type in the building model. See Placing a Decal in a View.

In Revit Structure, you can only define decal types. To place decals, use Revit Architecture or Revit MEP.