Snippet from build script to generate thumbnails: https://github.com/akmurray/aaronkmurray-blog-tools/blob/master/build/build-aaronkmurray-site.bat

aaronkmurray.com-generate-post-thumbnails.bat

REM Make thumbnails if necessary
FOR /F %%A IN ('dir /b "../../aaronkmurray-blog/img/blog/screenshots/" ^|findstr /liv "thumb"') DO (
  REM "SETLOCAL ENABLEDELAYEDEXPANSION" so that we can update variables inside a loop. Those variables are wrapped in "!" instead of "%"
  SETLOCAL ENABLEDELAYEDEXPANSION
  
  REM variables 
  SET thumbName=%%~nA-thumb-100.png
  SET thumbPath=../../aaronkmurray-blog/img/blog/screenshots/
  SET thumbPathAndName=!thumbPath!!thumbName!
  
  IF NOT EXIST !thumbPathAndName! (
    ECHO Creating thumbnail for !thumbName!
    convert.exe -thumbnail 100 !thumbPath!%%A !thumbPathAndName!
  ) ELSE (
    REM ECHO Already created thumbnail for !thumbName!
  )
)