Currently Being ModeratedMay 7, 2012 1:29 AM (in response to mabellucy)
Same method as in most DTP applications.
In Pages you trace the object with the pen tool, at the bottom of the shapes menu, select both the drawn shape and the image:
Menu > Format > Mask with selected Shape
Double clicking on the shape will then let you fine tune the points.
If there is a background to the image you select it and :
Menu > Format > Instant Alpha > Paint over the areas you'd like to mask
Control the Wrap with:
Inspector > Wrap > Text Fit
Currently Being ModeratedJan 23, 2013 12:35 PM (in response to mabellucy)
You can place a shape behind your graphic and make it editable in the usual way. Make sure you have grapic "Object Causes Wrap" selected. Then drag the points on it to where you want. Colour it to background colour so it is not seen. You can group it with the graphic afterwards if you want. This should acheive what you want to do.