Online converters earn their place for quick, one-off jobs: no installation, no configuration, works on any machine. Some run entirely client-side — Squoosh processes your pixels in the browser, so they never hit a third-party server, a meaningful distinction when you’re handling client photos or NDA assets. Others upload to a remote server; convenient, but the file has left your machine, so check the privacy policy first.
The horsepower lives on the desktop and the command line. GIMP handles conversion across virtually every raster format for free; ImageMagick and ffmpeg compress, resize and reformat entire directories reproducibly — and expose every knob the online defaults hide.
01The practical split
Familiar server-side names round out the category: TinyPNG offers a limited free tier with per-file size caps; Kraken.io handles batch uploads as a ZIP, also with free-tier limits. Both are convenient — and both mean your file travels.