It's easy to do pixel art in Minecraft. Pick a area in your map seed, preferably a flat one and using the image provided on this website, then start from the bottom up, follow the image pixel grid system & create the main frame as shown in image 3 bellow.
Then just add any related colour to your frame, in this case a creeper so any green blocks will do.
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| Pick a nice Place, Image 1 |
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| Start from the bottom up, Image 2 |
As you can see the odd blocks in the above image is use as a guide for block counting.
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| Just do the main frame, Image 3 |
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| Fill in the frame, Image 4 |
Random green colour block placement is the trick.
