title_body: How to convert epub/mobi to PDF without image distortion?
upvoted_answer: Converting from mobi to pdf is almost always going to be a problem. Both are rendered formats. The problem could come from anywhere. Two ideas:
  
  First, try to obtain an epub copy instead of a mobi file. It's easier to convert from epub to pdf than from mobi to pdf. 
  
  Try decompiling the mobi file (go to mobileread to find a tool that can do so). 
  
  Possibly there is a setting in Calibre to preserve the image ratios. But really, this is asking calibre to do the impossible.