Command Line Tool which is included in Astah installation folder enables you to export images and compare projects from Command-Line.

Export image files

By using -image option with astah-commandw.exe (for Windows) or (For Mac or Linux),
you can export diagram images as PNG, JPEG, EMF or SVG.
If you do not specify the image format, it exports in PNG format automatically.

[Windows] Export all the diagrams in the C:\input\hoge.asta.file to C:\output in PNG

astah-commandw.exe -image er -f C:\input\hoge.asta -o C:\output

[Mac/Linux] Export all the diagrams in ~/input/hoge.asta file to ~/output in JPEG -image all -f ~/input/hoge.asta -o ~/output -t jpg