Definitions (in laymans terms):
DPI: Dots per inch. The number of dots in a printedinch. The more dots the higher the quality of the print(more sharpness and detail).
PPI:Pixels per inch. Most commonly used to describe the pixel density of a screen (computer monitor, smart phone, etc) but can also refer to the pixel density of a digital image.
Resolution: Resolution is the measure of pixels in the display, usually expressed in measurements of width x height. For example a monitor that is 1920 x 1080 is 1920 pixels across and 1080 pixels down.
Higher resolution means more detail. Higher DPI means higher resolution. Resolution is not size, but its often confused with it because higher resolution images are often bigger, but that doesnt necessarily have to be the case.
Print:300dpi is standard, sometimes 150 is acceptable but never lower, you may go higher for some situations.
Web/Digital: DPI doesnt equate to digital its a print measure. It was commonly believed for a long that 72dpi was ideal for web. If you hear that its simply not the way things work. When talking digital, were concerned with the actual resolution. How that image prints is another matter.
Lets see it in action
If you are creatingimages to use for print and the images are too small the odds are the resolution wasnt high enough. Theimage might look huge on your computer but stillprint out quite small. To add to the confusion, your screenresolution will also determine how big the picture appears to you when viewing it on your computer.
A monitor set to 1024×768 will show an 1024pixel wide by 800pixel tall image as a full screen image. On a monitor that is 1920×1080 the image will only take part ofthe screen. Long story short, the image will look much smaller on that screen even though the image is the same size because the screen has higher resolution.
Here are a couple of quick examples to show you the difference, no matter what your monitor resolution, its all relative!
The first example below has a lot of detail.
The second example is at 72dpi but scaled up to the same size so you can see the difference in detail. The actual image would be about 1/4 the size when you go from 300dpi to 72dpi, but at the same height and width is where you can actually see the difference.