Change the DPI of a JPG or PNG to any value without touching the pixels — for printing and forms that ask for 200 or 300 DPI.
Only the DPI number inside the file changes — the pixels and quality stay the same.
DPI (dots per inch) is a number saved inside a photo that tells printers how big to print it. The pixels stay the same — only the print size changes.
print size (inches) = pixels ÷ DPI
The DPI value is written into the JPG (JFIF header) or PNG (pHYs chunk). The image is not re-compressed, so quality and pixel size stay exactly the same.
A 600×600 photo
No. It only changes the print size stored in the file. To get more detail you need more pixels.
Set the DPI here. If it also gives a size in cm or inches, use the Image Resizer with that unit and DPI.
No. Everything happens inside your browser on your own phone or computer. Your photos are never sent to a server, so it is safe for ID cards, documents and personal pictures.