ok next version.
this one is also simple
open another seperate image any will do just as long as its bigger then your template. http://upload.wikimedia.org/wikipedia/commons/b/b0/Mint-leaves-2007.jpg
Wiki Commons is a good source for stock images though I also suggest http://www.photos-public-domain.com/
resize the image so that it fits the size of your template, Do this by Menu/Image/Scale Image... set the height to 1046 and click scale.
copy the image to clipboard or [Ctrl]+[C]
step 3 .
Add second layer[Shift]+[Ctrl]+[N] to your template image set to transparent
copy your other image to this second layer and Anchor it [Ctrl]+[H]
Open the Layers Toolbox [Ctrl]+[L] (mine is always on)
select the base layer, thats your gray template. Fuzzy Select area outside the gray area, then select the top layer.
as you see your selection is still highlighted.
Right Click the layer in Layer Toolbox, Add Layer mask - set to White
Bucket Fill the to Black. now your image should be shaped like the template
Right Click Layer Toolbox And Apply Mask
step 5 Merge Visible Layers [Ctrl]+[M] and save. your done