Compressing a photo without it looking like a copy of a copy

A photo compressed once at a reasonable quality setting looks essentially identical to the original. The same photo, compressed, opened, edited, and re-compressed a few times over its life, starts showing blotchy artifacts around edges and color banding in skies and gradients — the compression damage compounds every time.

Why JPEG compression is lossy in a specific way

JPEG compression works by discarding detail the human eye is less sensitive to — subtle color variation more than subtle brightness variation, fine texture more than sharp edges — and that discarded detail is genuinely gone, not just hidden. Compress the same already-compressed file again and it discards more detail on top of an image that's already missing some, which is why repeated re-saving degrades a photo in a way that compressing once at a lower quality doesn't.

Picking a quality setting that actually holds up

• For photos going into a document or a webpage where file size matters, a moderate-to-high quality setting (70-85 on a typical 0-100 scale) is usually indistinguishable from the original at normal viewing sizes while cutting file size substantially.
• For anything you might edit again later — cropping, color correction, combining with other images — keep an uncompressed or lightly-compressed master copy, and only produce a heavily compressed version as the final export step.
• For images with large flat areas of color (screenshots, simple graphics, logos) a format that isn't lossy at all — PNG — often compresses better than JPEG anyway, since there's no fine photographic detail to discard.

What Compress Image actually does

Compress Image re-encodes your photo at a quality level you choose, running entirely in your browser using the same underlying image codecs your browser already has built in — nothing is uploaded to get a smaller file back. The tradeoff is the same one described above regardless of what tool does the compressing: it's a one-way reduction in detail, so keep an original copy of anything you might need at full quality again.