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How to combine images side by side on a Mac
By Himanshu Ranjan · Updated 8 November 2026
To put images side by side on a Mac, select them in Finder and run Combine › Combine side by side in FileDial, which makes one new image beside the first. For screenshots, Combine › Stack side by side… and Combine › Stack screenshots vertically… write one PNG in selection order. Everything runs locally.
Pick the tool for the job
There are three joiners in FileDial's Combine menu and they are not interchangeable. The differences are in how they size images and what they output.
- Combine › Combine side by side: one new image beside the first.
- Combine › Stack side by side…: one PNG, same height, left to right in selection order.
- Combine › Stack screenshots vertically…: one PNG, same width, top to bottom in selection order.
- Combine › Make a collage: one new image beside the first, for many pictures in a grid style.
Steps
Selection order matters for the stack tools, because FileDial says they join files in selection order. For a before and after, click the before image first and then Command-click the after. Run the tool and check the arrangement.
- In Finder, click the first image, then Command-click the others in the order you want them.
- Hold the right Option key to open the dial, or right-click and choose Open in FileDial.
- Choose Combine, then release on Combine › Stack side by side… for a left-to-right strip, or Combine › Combine side by side.
- Open the new image beside the first and check the order.
Before and after comparisons
Side-by-side images are the standard way to show a change: a redesign, a repair, a retouch or a renovation. Make the pictures the same height first, since Stack side by side… already normalises height. Use the same crop and framing for both so the viewer compares content, not composition.
Label them. A before and after with no caption can be misread, and a subtle mark such as Markup › Add watermark text… or the Edit photo… tool lets you add words like Before and After on each picture first.
Screenshots and documentation
For support docs, bug reports and tutorials, stacking screenshots vertically produces a single tall PNG with the same width, which is easier to attach than five files. If you only want a PDF, Combine › Combine into one PDF takes photos and PDF pages in selection order. For a printable overview of many photos, a contact sheet is a better fit than a long strip.
Stacked PNGs can be large. If the result will be emailed, run Compress › Compress afterwards, or convert to JPG if it has no transparency.
Making comparisons fair
A side-by-side image persuades, so be fair with it. Use the same lighting, the same framing and the same scale in both pictures. If the after photo was shot closer, crop the before to match with Resize › Crop… or Resize › Smart crop 4:5, so the viewer compares equivalent areas.
Match the sizes before joining. Stack side by side… normalises height, but wildly different resolutions can still produce one soft half. If one picture is much smaller, consider Resize › Upscale 2× on it, but be honest that it has been enlarged.
Finally, think about the file you are making. A wide strip of two large photos may be thousands of pixels across, which is more than most screens show. Resize it to a sensible width with Resize › Resize to 2048 px or Resize › Resize… and compress for sharing.
- Same framing and scale in both halves.
- Match resolution first.
- Resize the finished strip for sharing.
When FileDial is not the right tool
If you need annotations, arrows, text boxes or precise spacing, use a layout or design app, or Markup › Edit photo… on the joined result, which adds text, arrows, shapes and a pen. FileDial's joiners are for fast, consistent results, not for custom layouts.
Common mistakes are joining pictures with different resolutions, which gives one blurry half, and forgetting selection order, which swaps before and after. Check the order in Finder before you run it. If the joined image will be shared widely, run Privacy › Remove all metadata on the result, because combined images can inherit details from the first picture's file.
A quick decision guide: for two pictures, use Combine side by side. For a strip in selection order, use Stack side by side… For a tall run of screenshots, use Stack screenshots vertically… For many photos in a grid-like image, use Make a collage. For one file that holds pictures as pages, use Combine into one PDF. If you need captions beside each picture, add them first with Markup › Edit photo… so the joined image already carries the words.
Local processing
Comparison images often show unreleased work or private rooms. FileDial joins them on your Mac and never uploads them.
Questions
How do I put two photos side by side on a Mac?
Select both in Finder, in the order you want, and run Combine › Combine side by side or Combine › Stack side by side… in FileDial. It writes one new image. Preview can also do it manually by copying and pasting, but that is slower and less exact.
Does selection order matter?
For the stack tools, yes. FileDial says Stack side by side… joins left to right in selection order and Stack screenshots vertically… joins top to bottom in selection order. Click the first image, then Command-click the rest in your intended order.
What file format does the combined image use?
FileDial describes the stack tools as writing one PNG. PNG is lossless, so these files can be large for photographs. Convert the result to JPG or compress it if you plan to email or upload it. Stacked PNGs of photographs get large quickly, so convert the result to JPG or run Compress › Compress before emailing.
Will my originals be changed?
No. The combined image is a new file beside the first original, and the originals are left alone unless a tool says so up front. Undo is available on every result. Selection order controls the result, so click the images in the order you want before running the tool.