Image no longer loading in posts

I am getting report that images are no longer loading in post,instead it display an error message

Image error
convert: improper image header `-' @ error/png.c/ReadPNGImage/3647. convert: option requires an argument `-write' @ error/convert.c/ConvertImageCommand/299

Can anyone tell me what causing this error and advise how to fix it?

Thank you
BIll

convert is still working on the server

ns(313):[/]-#convert --version
Version: ImageMagick 6.7.2-7 2017-03-22 Q16 [www.imagemagick.org]
Copyright: Copyright (C) 1999-2011 ImageMagick Studio LLC
Features: OpenMP

I got it figured out.

When I upgrade PHP, I had to recompile the imagick php module. I thought the upgrade would use the same modules.