Merge Images
Combine two or more images onto one canvas — side by side, stacked, or overlaid with adjustable opacity. Nothing leaves your browser.
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How merging images works
Merge Images composites two or more pictures onto a single HTML canvas entirely in your browser — nothing is uploaded anywhere. Choose side by side to place images left-to-right, stacked to place them top-to-bottom, or overlay to layer them directly on top of each other with an adjustable opacity slider (handy for comparing two versions of an image or creating a ghosted double-exposure effect). Reorder images with the up/down arrows before merging — order matters for side-by-side/stacked placement and determines which image is the base layer in overlay mode. The result can be exported as PNG (with transparency), JPEG, or WebP. For combining images into a single scrollable strip after merging, or resizing the output afterward, try the Image Resizer.
Built and maintained by Meet Shah · Last updated
What this tool is used for
- Putting a before and after screenshot side by side in one file.
- Stacking several screenshots into a single attachment for a ticket.
- Overlaying two images at partial opacity to compare them.
- Combining a set of panels into one graphic for a document.
- Producing a single image where a platform allows only one upload.
Frequently Asked Questions
- How are the images combined?
- Drawn onto one canvas in sequence, either side by side or stacked, then exported as a single file. Nothing is uploaded — the images are decoded and composited locally, which is why it works offline and on screenshots you would not send anywhere.
- What happens when the images are different sizes?
- The canvas takes the largest dimension on the joining axis and the sum along the other, so a smaller image leaves empty space rather than being stretched. Scaling them to match first is usually what you want if the sizes differ a lot.
- Which output format should I choose?
- PNG when any source has transparency or contains text and sharp edges; JPEG when everything is photographic and file size matters. Merging two PNGs into a JPEG flattens transparency onto a background colour, which is the surprise to watch for.
- Does merging lose quality?
- Only through re-encoding. The pixels are copied exactly onto the canvas, so a PNG output is lossless; a JPEG output re-compresses everything including sources that were already lossy, which stacks artefacts from both generations.
- Is there a size limit?
- Browsers cap canvas dimensions — commonly around 16,384 pixels per side, lower on iOS — and exceeding it produces a blank result rather than an error. Merging many large photos into one strip is the case that hits it.
Common errors and gotchas
- Merging images of different dimensions without deciding how to align them, which leaves uneven gaps.
- Re-encoding lossy sources, which compounds artefacts on both halves.
- Producing a combined image too large for the destination's size limit.
- Losing transparency by flattening onto an unintended background colour.
- Merging at differing pixel densities, so one half looks sharper than the other.