Maybe an auto re-sizer that creates a thumbnail of the image if it is too wide for the post?
Eg. My banner in this post is cut off:
https://mobpb.forumotion.com/off-topic-f6/banner-needed-t4.htm#34
Eg. My banner in this post is cut off:
https://mobpb.forumotion.com/off-topic-f6/banner-needed-t4.htm#34