I have tried Multi Monitor Manager & other programs to do this but the image on the 23" AOC 1920x1080 is always off. I came across a thread here & tried to follow it but haven't been able to get this right. My new iMac is 27" 2017 model which I have AOC 23" attached. I gather that the iMac is 5120x2880 and the AOC 1920x1080. I was advised to try to use Photoshop to do this with layers and boxes which would include the bezels but I haven't a clue how to do this. I have included the thread below - if anyone can advise that would be amazing. This is what Im trying to do and think I have the resolutions correct but may need help with that to confirm I have but mainly don't understand how to do this in Photoshop #2 ↑ Hello! I currently have a 15" retina MBP with a 24" 1080p display as a second monitor. I would like to make a wallpaper that spans across both displays, with the bezels on each representing a break in the actual image. I am running into difficulties in making the image line up correctly across the displays. Here is how I have my monitors laid out: View attachment 643866 Resolutions for each: rMBP: 2880x1800 (but I am currently running the "Default" setting, which "looks like 1440x900") 24" display: 1920x1080 Any help would be greatly appreciated. Thank you so much!! Click to expand... I was in your shoes a few years ago. The real trick is match the pixel density on each screen so that it really looks like each monitor is a window looking onto the scene. Some simple proportional math will help you with that. The effective pixel density of the retina display is (2880^2 + 1800^2)^(1/2)/15 = 226.4155 pixels per inch (ppi). The pixel density of the 24" display is (1920^2 + 1080^2)^(1/2)/24 = 91.7878 ppi. You have to increase the size of the image you use on the 24" monitor to match the pixel density of the laptop screen. So the horizontal resolution of the image you need on the 24" monitor is 1920/91.7878*226.4155 = 4736. Similarly, the vertical resolution is 2664. Now that you know the working pixel density (226.4155), you need to measure the width of the bezels in inches and then multiply by 226.4155 to know how much space in the image to allow for them. For example, if each bezel is 1/2-inch wide, then you have one inch or 226 pixels of gap between your images. Now, use your favorite image editor that supports layers to make some boxes of the right pixel sizes to represent your laptop screen, the external monitor, and the bezels. Arrange these boxes on top of a large image for the wallpaper and save out the two images you will need for the wallpaper: one image for each display. This will allow the images to line up on both monitors. In your case, you will need a starting image of 2880 + 226 + 4736 = 7842 pixels wide and 2664 pixels tall. --- Post Merged, Aug 8, 2016 --- By the way, here is a link to some very large images you can get started with. http://osxdaily.com/2013/02/15/12-stunning-high-resolution-wallpapers/ If you already have images you want to do this with that are not large enough for full retina resolution, then divide your working pixel density in half (113.2078) and use the effective resolution of the retina display (1440x900) for your image size calculations.