Side by side, stacked or in a grid
Side by side puts the images in a row, left to right. It is the classic layout for a before and after, for two versions of a design, or for the front and the back of a card shown together. So that the row looks tidy, the images are brought to the same height, each keeping its own proportions.
One below another stacks them in a column and brings them to the same width. That is the layout for joining several screenshots of a long chat or a web page into one tall picture, or for placing a photo above its caption.
The grid arranges the images in 2, 3 or 4 columns and as many rows as needed: a small contact sheet of product photos, the pictures from a trip, or the steps of a tutorial.
Order, spacing and background
The images are merged in the order shown, and you change that order by dragging them. Put the “before” on the left and the “after” on the right, or sort the screenshots from first to last.
Spacing is optional. Without it the images touch, which works for screenshots that continue one another. With spacing, a band of background separates them, and you choose its color: white, black or transparent. White suits anything you will print or paste into a document, black gives a gallery look, and transparent lets whatever is behind the image show through. A transparent background needs PNG or WEBP as the output format, because JPG cannot store transparency.
One file instead of several
Plenty of forms and websites take a single file where you have two. The upload field accepts one image, but your ID has a front and a back; the marketplace shows one main photo, but you want buyers to see the product from two angles; the teacher asked for one picture of homework that took three pages. Merging the pictures first solves it.
It is also a simple way to make a comparison for social media or a slide, without design software. If what you need in the end is a document, send the result to “JPG to PDF”, or put each image on its own page with that same tool instead of merging them.
Size of the result
Joining large photos produces a very large picture. Several full-resolution phone photos in a grid can add up to more pixels than a browser handles comfortably. For that reason, when the combined image would go beyond roughly 16 megapixels, it is scaled down in proportion. Nothing is cut off and the layout doesn't change; the whole picture is simply made smaller.
For photos, JPG or WEBP give lighter files. PNG is the better choice for screenshots and graphics with text. If the file is still too heavy for where it is going, pass it to “Compress image” and set a size in KB.
Your pictures stay with you
The images are combined in your browser, on your own device. They are not uploaded and no copy is kept, which matters when they are ID cards, receipts or private conversations. It's free, with no account, no watermark and no limit on use.