Jpegmini Pro Portable ((free)) -

The Ultimate Guide to JPEGmini Pro Portable: Maximum Compression, Zero Compromise, Complete Mobility

Legal vs. Grey Area: The Truth About "Cracked" Portables

2. Caesium Image Compressor (Open Source Portable)

3. RIOT (Radical Image Optimization Tool)

Tagline (one line) Shrink JPEG files up to 80% with original quality preserved — portable, fast, professional.