Thank you guys, feel free to use this script in your themes. Could you please test it at your demo servers for first and then let me know if it works ? It should be 100% bulletproof, because it’s using built-in WordPress functions to resize the images. But I want to have a proof, because I don’t want to be under pressure when you release theme and find a bug after that 
SCRIPT UPDATE
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now you can resize all images hosted at your server, not only in wp directory
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consulting remote images with my programmer friends