Images - PPI and DPI

For some, there seem to be some basic misunderstandings about images, PPI (pixels per inch) and DPI (dots per inch), and how this is considered in layout.

Starting with the Image Source
Let's imagine that we have taken a photograph with a camera. The camera will create an image file with a certain density of PPI, depending on scanner or camera settings. Once the file is created, this sense of density or PPI has no meaning, and what you really have is the data for an image having a width of a number of data points of width (referred to as pixels), and a height of a number of data points.

At this point, the PPI is dependent on the display device and resolution.