How can I change the resolution or DPI of a photograph?

from 150 DPI to 300DPI.

I'm using Windows XP.How can I change the resolution or DPI of a photograph?
Your operating system will not effect your image quality. That is first determined by the resolution you set in your camera. Always shoot at the highest resolution and size your camera affords. You can always make your images smaller and with less resolution later, but not the other way around.



Use the software that came with your camera and you should be able to adjust size, resolution, JPEG compression and a lot of other things.How can I change the resolution or DPI of a photograph?
A photograph in the computer doesn't have a DPI (dots per inch), it only does when you print it. When you print a photo on an inkjet photo printer, the printer software automatically changes it to the resolution of the printer, depending on what size you're printing it.



But if you want to change the resolution of a picture, you can do that with photo editing software like Photoshop or similar. Even some photo 'viewers' can do this, like ACD See. It doesn't make the photo any sharper, it just makes more pixels.
windows xp will not change anything. You need a photo processing software such as photoshop. Any type of photo editing software will reduce the size of a photo. However, you can not take a low resolution photo and make it high resolution just by changing the DPI. You have to alter the image size in your camera to large image so that the photos will be saved at 300dpi.