It will allow up to 140 pixels high. My sig is now 120 pixels high and I think that is best.
You might want to try single spacing your wording to make your sig's overall height shorter.
what I mean by "your sig is not visible" is that is is way too dark...I would think you would want a bright pic in your sig....most people wouldnt be able to tell it is an arowana.. 120 pixel height is perfect in my opinion...not too big, not too small
I don't have a problem adding images but I also try to keep them small. Different sites allow for different size images, some sites let you post huge pics and others don't. Presumably, this site is the latter type.