Gimp Tutorial for using Masks

First of all open a new canvas

then open your chosen mask as a layer

Re size the Mask to your required size.

Then you need to open up your photo in a new window so it looks like this




Then still in your photo - use the rectangle toll and chose the area you would like and then click crop to selection

Then resize your photo to match about the same size of your mask

then move the image to the top corner and click copy visible like this









then make sure your clipboard is selected in your patterns palette




Now go back to your Mask layer and in the tools palette right click on the mask layer and click ALPHA TO SELECTION



The click EDIT - FILL - FILL WITH PATTERN



Finished Result