Merge Images

Merging images draws several pictures onto one canvas and gives you a single file back. It is what you want for a before and after pair, a set of screenshots that belong together in one upload, a photo grid for a post, or any place that accepts one image where you have three.

The part that sounds trivial and is not is that your images are almost never the same size. A photo from a phone might be 4032 by 3024 and a screenshot 1170 by 2532. Drawing both at their native size into one strip gives a result where one is four times the height of the other, which looks like a mistake rather than a layout. Every mode here normalises first, on whichever axis has to line up.

Side by side matches every image to the tallest one's height, so the tops and bottoms align and each picture keeps its own aspect ratio by taking the width that follows. Stacked does the same in the other direction, matching to the widest image. Neither mode enlarges anything beyond the largest input, so no image is upscaled into softness just to match a neighbour.

A grid has to match both axes, so it needs a second decision: what to do when a picture does not have the cell's shape. Contain fits the whole image inside the cell and leaves space around it, which keeps everything visible and gives a slightly ragged grid. Cover fills the cell completely by cropping the middle out of the picture, which gives the even grid that reads as a collage and loses the edges. Neither is correct in general. Contain for anything where the edges matter, like screenshots or documents; cover for faces and scenery, where a centred crop is usually fine.

One practical limit is worth knowing. Twelve photos from a recent phone at native size make a canvas over 12,000 pixels on a side, and browsers refuse to allocate a canvas that large, which is the usual reason a merge tool fails with a blank result. This one measures the finished size first and scales the whole layout down to something a browser will draw, rather than failing. The output is still far larger than anything a web page needs.

Everything runs in your browser. The images are decoded, drawn and exported locally, so a set of screenshots with account details in them, or photos you have not published, do not pass through anyone's server to become one file.