Both Stock Photo's by

Most Base Sizes for full bodys vary from around 200 Pixels - 500 pixels at the largest, most people won't use bases any larger then that


--Photoshop
Edit < Image Size
Once you've clicked that, this should appear, General size for bases is around 500 at VERY largest and 200 at smallers, but that's just what most people use

--MS Paint
Image < Stretch / Skew
This one is a little harder, You need to put in the percentage that you are shrinking it down, if image is around 1200 pixels 25% seems to make it around 200-300 pixels tall, mess around with it, if you make it too small hit Ctrl+Z and it will undo the changes and you can choose a different percentage, but be warned, you can only go back 3 times.

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ok, sorry its not perfect XD;;; but this gives you then general idea, feel free to experiment with sizes

i messed up in some spelling and stuff in the image, but i fixed it in comments xD;;;

*edit*

fixed it i think XD;;;