DPI is often misunderstood, especially when it comes to images used for the web. What is it and when do you need to think about this? Do you need 300DPI? Should you care? Here is a short description and some examples of use.
DPI stands for Dots Per Inch and is a print setting.
In printing, a ‘dot’ means a dot of ink. So 300dpi means 300 dots of ink per printed inch. As you can imagine, the more dots of ink, the clearer the image will be.
For example: A 900×900 image at 300DPI will automatically print at 3×3 inches i.e. 900/300 = 3 inches. You can print the same image at 72DPI but it’ll print at 900/72 = 12.5 x 12.5 inches.
72DPI is too low for print and the image will be blurry. 300DPI is ideal for printing but even a lower dpi like 240 is also ok.
So if you’re using an image for the web, DPI doesn’t matter. The image will look the same on the screen whether it’s 10DPI or a 1000DPI.
For more information, here is a wikipedia link on dpi.
For online images, color, clarity and image size is all that matters. For print, you need an image that is big enough to print at the size you want i.e. if you want to print an image on a 10×10 inch paper at 300DPI, you need an image that is 3000x3000px in size.