You can enable OPI on a picture-by-picture basis when you import a picture, when you modify an imported picture, or when you use the OPI tab of the Usage dialog box (Utilities menu):

• When you import a picture (File > Import Picture), check Use OPI to enable OPI substitution for the picture.
• Select a picture that has already been imported into the layout, and then choose Item > Modify and click the OPI tab. Check Use OPI to enable OPI substitution for the picture.
• Choose Utilities > Usage > OPI tab to display a list of all pictures in the layout. If a picture is checked in the OPI column, that picture is set to be exchanged.