How to detect the screen DPI using JavaScript
The only way I found till now, is getting the offsetWidth, offsetHeight of a test div element with height and width of one inch:
http://www.infobyip.com/detectmonitordpi.php
dpi
How to set a specific ppi to a 1-bit color-depth PNG image?
I am trying to set a specific resolution (PPI) to a PNG file, but I am always getting N/A value
Photoshop setting up wrong DPI and size when opening AI file
When I try to open AI file using Photoshop, it shows me wrong image size and DPI.
What DPI should be used for what situations?
I’ve been seeing the word ‘DPI’ pop up quite a lot when I export my work out in Photoshop and Illustrator. While I know that DPI stands for ‘dots per inch’, and that if you have too low of a DPI on an image, heavy pixellation occurs if you try to zoom in, what would be the optimal DPI for what situations?
Is it mandatory to keep images at 72 dpi for web design?
I have been designing web banners for more than a year but never considered the DPI.
Will increasing the dpi of my image (without re-sampling) hurt print quality?
I’d like to start making prints, but all of my work is set at a resolution of 72. Are there any negative effects to increasing the resolution to 300?
I’m very new to this, but from what I’ve read so far: higher res = nicer looking prints.
DPI Vs. PPI Vs. Image dimension, what should be taken to consideration?
I’ve been really facing this problem and I have found a similar link, that does not really address the problem. First of all, I’d like to mention that I use blender and GIMP for most graphics that I design and please read all the way through.
Why does Photoshop call ppi “resolution”?
There are some things in Photoshop’s “new” dialog window that I find troubling: 
Illustrator: View -> Actual Size smaller than life size
I’m using Illustrator CS6 on OS X. When choosing View -> Actual Size, the displayed elements are smaller on the screen than their actual size, say in centimetres. How can I “calibrate” Illustrator to my screen’s resolution (dpi) so that it can display objects at life size when using 100% zoom?