What is Image Compression?
TL;DR: Image compression reduces file size by removing redundant or imperceptible data. Lossy compression (JPEG) permanently discards some data for smaller files, while lossless compression (PNG) reduces size without any data loss.
JPEG compression works by dividing images into 8x8 pixel blocks and applying DCT (Discrete Cosine Transform) to discard high-frequency details the human eye can barely see. At quality 80%, file size drops 80%+ with minimal visible difference.