How to Combine Images Side-by-Side Using Preview on macOS

When you are operating on a macOS workstation and you must rapidly combine two separate image files into a single, unified geometric canvas (e.g., placing a front and back ID scan side-by-side), booting a massive, memory-heavy application like Adobe Photoshop is mathematically inefficient. To force the native macOS Core Graphics engine to execute a rapid canvas expansion and pixel injection, you must deploy the Canvas Modification matrix within the Preview application.

Executing the Canvas Expansion

The Preview engine contains a deeply embedded capability to mathematically expand the borders of an image and accept raw pixel data from the system clipboard into the newly created void.

1. Locate your first target image file (Image A) in Finder and double-click to open it natively in Preview.
2. Look at the absolute top menu bar. Click Edit, then Select All (or execute Cmd + A). The engine will highlight every pixel.
3. Click Edit, then Copy (or execute Cmd + C). This injects the Image A payload into volatile memory.
4. Open your second target image file (Image B) in a separate Preview window.

Deploying the Pixel Injection Vector

5. In the Image B window, you must mathematically expand the canvas to make room for Image A. Click Tools in the top menu, then select Adjust Size….
6. A geometric modal will spawn. Uncheck the box labeled Scale proportionally.
7. Identify the current Width. If you want to place Image A side-by-side with Image B, mathematically double the Width integer (e.g., change 1000 pixels to 2000 pixels). Click OK.
8. The Core Graphics engine will instantly expand the canvas, filling the new void with a default background color (usually white or transparent).
9. Click Edit, then Paste (or execute Cmd + V).
10. The engine will inject the Image A pixels from the clipboard onto the expanded canvas as a floating geometric layer. Click and drag Image A to the exact desired physical coordinate (e.g., the right half of the canvas).
11. Click anywhere outside the image to mathematically flatten the layer, then press Cmd + S to permanently save the unified file.