About the joiner
MergePicture does one thing: it puts pictures next to each other and gives you back one picture. That is the whole product, and keeping it that small is a decision rather than a limitation.
Why one operation
Most tools that will join two pictures will also crop them, filter them, add text to them and hunt for a file size, and each of those features is one more thing between you and the join. The trade in the other direction is that a tool doing one operation can afford to answer the awkward questions properly — what happens when the heights don’t match, what happens to a colour profile at a seam, what happens when the result is taller than a browser will draw. Those are the questions that make a join look wrong, and they are all in the Fit step.
What it deliberately does not do
It does not mix two frames into each other so both show through. It does not place a small element on top of a photograph. It does not put a repeated protective mark across a batch, or fill a chosen template with photos, or cut a picture into pieces. Pictures here touch and never cover each other. The one place a file size is chased is the photo-and-signature page, because exam forms state a kilobyte range and a file outside it is refused — there the target is searched for honestly and the page says when it cannot be met. Anything else we have not built yet, we say so plainly rather than shipping a thin version of it.
How it is built
It is a static site with no server behind it. Pictures are read by your own browser, arranged on a canvas by your own browser, and turned into a file by your own browser. There is no upload step because there is nothing to upload to: no account, no queue, no storage. The measuring work behind the long-screenshot mode runs in a background thread so the wizard stays responsive while it thinks, and the code that does it is fetched only when you choose that mode.
The consequence, which is worth stating: everything is limited by the device in front of you. A phone with little memory will refuse a hundred large pictures where a desktop would not. We would rather tell you that in a sentence than hand you a truncated file.
Who makes it
A small, independent team builds and maintains MergePicture, and merging pictures is the whole of what it works on here. There is no account, no paid tier and no advertising — the site is free to use, and the pictures you open are never ours to see.
Getting in touch
If a join comes out wrong, the useful thing to send is the sizes of the pictures that went in, which of the four sizing policies was set, and what you expected instead. Write to hello@mergepicture.com. Please don’t attach the pictures themselves — we would rather not have them, which is rather the point of the whole thing.