Resampling jpegs inside a PDF (to shrink/reduce file size)

My wife is applying for various teaching jobs. Most of the positions require uploading documents to various school board applicant tracking systems. I carefully prepared the documents for her, also wanting to keep them for historical archival purposes. The uploads produce a bizarre error. Contacting the site administrator, we find out that there is a 1 megabyte file size limit on uploads and this is what produces the cryptic error. Sigh. (To add insult to injury, after resampling the scanned PDFs, it then turns out there's also crazy filename limitations... so all the nice descriptively  named files had to be renamed to eliminate various characters, and maintain a certain length). These are the gatekeepers of our children's education.

But I digress.

This info is a lot of places on the net already, but I want to add it here for my own reference as I've forgotten the simple command line a few times already and had to re-search it. 

In short, use ghostscript:

gs -sDEVICE=pdfwrite -dPDFSETTINGS=/ebook -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf

The PDFSETTINGS presets equate to the following resolutions:

• /screen ... screen-view-only quality, 72 dpi images 
• /ebook ... low quality, 150 dpi images
• /printer ... high quality, 300 dpi images 
• /prepress ... high quality, color preserving, 300 dpi images
• /default ... similar to /screen

Other suggested command line arguments made various places:

• -dCompatibilityLevel=1.4 
• -dColorImageResolution=38 -dColorImageDownsampleType=/Average -dGrayImageDownsampleType=/Average -dGrayImageResolution=38 -dMonoImageResolution=38 -dMonoImageDownsampleType=/Average -dOptimize=true -dDownsampleColorImages=true -dDownsampleGrayImages=true -dDownsampleMonoImages=true -dUseCIEColor -dColorConversionStrategy=/sRGB
• -dMaxSubsetPct=100

This page is quite good for further tips (such as recompressing with lossless compression).