Quick and dirty web image optimization

Given a large pile of images that nominally live on a web server, I want to make them smaller and more friendly to serve to clients. This is hardly novel: for example, Google offer detailed advice on reducing the size of images for the web. I have mostly JPEG and PNG images, so, jpegtran and optipng are the tools of choice for bulk lossless compression.

To locate and compress images, I’ll use GNU find and parallel to invoke those tools. For JPEGs I take a simple approach, preserving comment tags and creating a progressive JPEG (which can be displayed at a reduced resolution before the entire image has been downloaded).

find -iname '*.jpg' -printf '%P,%s\n' \
-exec jpegtran -o -progressive -copy comments -outfile {} {} \; \
> delta.csv