Add Outline to Image (Sticker Outline)

The thick white border around a die-cut sticker, the coloured rim around a cut-out product or character, the outline that makes an emoji pop on a busy background — all of them follow the shape of the picture, not its rectangle. This tool measures how far every pixel is from the shape's edge and paints an outline of the exact width you choose, outside, inside or centred on the edge, with smooth anti-aliased curves and an optional drop shadow. It works on transparent PNG, WebP, GIF and SVG images, all in your browser.

How to use this tool

1. Choose one or more images with a transparent background.
2. Set the outline width and colour (white is the classic sticker look).
3. Choose outside, inside or centred.
4. Optionally add a drop shadow.
5. Download the PNG; the canvas grows so the outline is not cut off.

Formula

outline opacity = clamp(w + 0.5 − d, 0, 1), where d = distance from the pixel to the nearest shape pixel

d is the exact Euclidean distance, computed for every pixel with a two-pass distance transform (Felzenszwalb and Huttenlocher), so corners become smooth arcs and the width is the same in every direction. A pixel belongs to the shape when its opacity is at least the edge threshold. For an inside outline the distance is measured the other way, from each shape pixel to the nearest transparent pixel.

Example

A 600 × 600 transparent PNG of a cat with a 12 px white outside outline becomes a 626 × 626 image (12 + 1 px added on every side). A pixel 6 px outside the cat is fully white, one 12 px away is half-covered (the smooth edge), and one 13 px away stays transparent.