Most masks can not be used in MMS but need to be done in other
programs that have the "clipping" ability. Some of the
designers have modified a way to use a mask in MMS (Albums to
Remember and Indigo Designs) They are actually very easy to
use. You bring them in as embellishments, put a photo sized
to fit the opening and then just use the "send it backward" button
to use it. Here's a link to a free one from Albums to
Remember to
try http://www.mymemories.com/store/display_product_page?id=ARBP-EP-1107-4996
If you have a program that does use traditional masking you can
save it as a png and bring it into use with MMS as an
embellishment.
Remember that the MMS shop also caters to ALL programs so
that is why they do sell the traditional masks in their shop.
Hope that helps.