Not sure about for making webcomics but The GIMP is a good free art program

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Screw the dead, I'm joining the living!

I'm Fire Lord Ozai in deviantART's Official Avatar: The Last Airbender Crew

i heard about a weird program the other day that might be what you're looking for! it was called... the photo shop? or something like that. i've never heard of it before but apparently it's good!!!!!!

xox

have you tried "the photo shop", everyone is saying it is good! theres also another program called water works i think its by a company called abode or something anyway good luck!