How much of this image do I need to modify in order to avoid copyright violation?
OP is explaining for not having permission on the material his post is related to. (unkowingly, probably but that doesn't matter)
So the contents he is embedding and linking to he had no permission to publicate and posting it here also violates the terms of the CC BY-SA 3.0 license, as I mentioned in a comment. So his post should be removed as soon as possible.