convert test.jpg
\( +clone -crop 200x1000+0+0 -sample 100x\! +repage \) -geometry +100+0 -composite
\( +clone -crop 200x1000+800+0 -sample 100x\! +repage \) -geometry +800+0 -composite
\( +clone -crop 1000x200+0+0 -sample x100\! +repage \) -geometry +0+100 -composite
test_result.jpg