We should keep the same aspect ratio than the original. Can you try to set your page with to 612 instead of 700 and see if it makes a difference?
You can also send the image to me (email@example.com) so that I can try this on my side.
After much experimentation, I've determined it to be an odd glitch with program. I won't bore you with all the weirdness I uncovered, there was a lot, but I will let the next person who stumbles upon this thread know how I fixed it for my situation.
I deleted the header completely and rebuilt it. Problem solved.
I determined that resizing the image in any way within the program cause the aspect ratio to go wacky.
It shouldn't though. If you send me your image and the step to reproduce I can log a bug on our side.
I had a similar problem (and solved it):
I combined (right click on selected files > "Combine supported files in Acrobat...") .jpg images to a PDF binder using Adobe Acrobat X Pro.
Image source: http://www.kultpower.de/archiv/heft_powerplay_1992-03
The result was a PDF with horizontally bloated pages that did not match the aspect ratio of the raw images.
Why is that so?
Unlike Foxit PhantomPDF, Adobe Acrobat uses EXIF metadata (ExifImageWidth, ExifImageHeight) stored in the image header instead of the real dimensions of the File (ImageWidth, ImageHeight).
Windows users can verify EXIF info by using for example the free tools XnView, Exifier or best ExifToolGUI.
In my case, the image dimensions were 1200x1710 (real actual dimensions) and around 1469x2084 (EXIF metadata).
Now how can that be - this does not make any sense ?
Well, obviously, the original file had larger dimensions and was resized without deleting the EXIF dimensions.
Because Acrobat uses the EXIF info intstead of the actual dimensions, the PDF looks distorted as a result.
Again, Foxit Phantom uses the actual image dimensions when creating PDFs.
How to solve the issue:
In case you have image files with different dimensions, the easiest way to fix this is by selectively deleting EXIF metadata using:
1) PhotoShop for single files (File > Save for Web & Devices > set “Metadata” to “None”: http://photographylife.com/how-to-delete-exif-data#ixzz2i0wFMNpE
2) ExifToolGUI (free) for multiple files in a folder: ExifTool direct > Command: -r -Exif:all= ( http://u88.n24.queensu.ca/~bogdan/ )