The photo you attached is 10" x 14" at 72 dpi. I think Minnie is right, your best bet might be to go to a kinko's and "test" one and see how large you can push it. I can make it any size you want, but since I'm not working from the original and it has been saved more than once, I wouldn't trust sending it away to do a large size print.
It is a very cute poster though ;-)
Kinko's is close. Do you think we can likely get an 18 x 24 from it? That would be big enough for sitting an easel I think.
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