Compress a JPG
Smaller, and still sharp.

A JPG is already compressed — that is the whole point of the format — so the question is never whether to compress it but how hard. Phone cameras and most editors save at a quality of around 92 to 95, which is far higher than anyone can see. Bringing that down to 75 or 80 typically halves the file and leaves an image most people cannot tell from the original.

JPG is lossy, so re-encoding always discards something. The loss is not cumulative in a way that matters if you do it once, but it does compound: saving the same photo five times at 80 looks worse than saving the original once at 80. Always start from the largest, least-edited copy you have rather than from a file that has already been through this a few times.

Quality is only half the story, and usually the smaller half. A photo straight off a modern phone is 4000 pixels wide, which is roughly four times the pixels a full-width web image needs. If a JPG is still too large at a quality you are happy with, it has too many pixels rather than too much quality — resize the longest edge to about 1600 px for a hero image or 1200 px for anything else, and the same quality setting buys you a much smaller file.

One thing worth knowing about the format: "quality 100" is not lossless. JPG throws away colour detail at every setting through chroma subsampling, because the eye notices brightness far more than colour. That is why a screenshot of text looks smeared as a JPG at any quality, and why PNG or WebP is the right choice for flat colour and lettering.

If you need to keep every pixel exactly as it is, JPG re-encoding is the wrong approach entirely — lossless JPG optimisation exists and rewrites the file's internal tables without touching the image, but it typically saves only a few percent up to around ten. This tool re-encodes, which is why it saves so much more.