You are best off using a graphics manipulation package e.g. Photoshop, to
make a mask and then porting the result into your Word document. It will give
you help and provide options e.g. soft edges. If you really want to do it in
Word just create freeform solids over the top of your picture. Fill them with
white and line colour white and play around with Edit Points to get as close
into the bit of the picture you want to save.
