Is it 72 DPI or 300 DPI?

Everyday I am asked questions about digital photography and digital imaging questions in general. I am always happy to help educate customers and photographers. However, one question keeps coming up. “Why are my images only 72 DPI?” I hope that I can help shed some light on this question.
DPI stands for dots per inch. In the printing world 300 DPI is commonly used to create sharp beautiful images at a specific size. Many misunderstand that if the digital file does not say 300 DPI that the file is too small or it is less sharp. This misunderstanding is amplified by using programs like Adobe Photoshop where a customer may view a file that says 72 DPI however, the file is very large and perfect for printing. While DPI is important the more important measure of a digital file are the pixel dimensions. The combination of the DPI and pixel dimensions determines the actual printing or document size. The following will illustrate this idea.
Figure A
The image displayed opens in Photoshop as a 72 DPI image but look at the pixel dimensions and document size.

Figure B
Now this is the same image as above displaying 300 DPI. Notice that the pixel size has not changed but only the document size.

How is this done you ask? Simply deselect the resample box and change the DPI to 300. You will see how the document size and DPI are linked without changing the actual pixel dimensions of the file.
On Fotolia every image displays the pixel dimensions and the document size at either 72 DPI or 300 DPI as displayed below.

Here is some information to think about when you are working on your next project.
1. Ask yourself how big you really need the image. What is the layout size of the image?
2. Then find out what DPI you need from your printer, website, or artist. (300 dpi is common for printing, 72 DPI for web, but this can vary with each application)
3. Then determine if the image you have selected will match your needs if used at that DPI.
I hope that this little bit of information has been helpful.