1. Reduce the pixel dimensions
This is the biggest saving and the one people skip. A modern phone photo is around 4000 by 3000 pixels, 12 million of them. A web page or a form almost never needs more than 2000 pixels wide. Halving both dimensions cuts the pixel count to a quarter. Use the resizer to set a sensible width.
2. Choose the right format
A photograph saved as PNG is the usual culprit behind an enormous file. Saving it as JPG or WEBP often shrinks it by 80 to 90 percent with no visible change. Keep PNG for graphics and transparency. The guide to JPG, PNG and WEBP covers the choice.
3. Lower the quality a little
At quality 100 a JPG is mostly wasting bytes on detail nobody can see. Dropping to 80 or 75 usually halves the file with no difference you could point to. Below 50 you start to see blocks and smudging. The compressor lets you try values and see the saving.
When you need an exact size
If a form says the picture must be under a certain size, guessing at the quality is slow. The target size tool tries values for you and stops at the highest quality that fits.
Things that do not help much
- Removing metadata saves a few kilobytes at most, though it is worth doing for privacy.
- Saving the same JPG repeatedly makes it worse without making it smaller.
- Changing the DPI does not change the file size at all.