Overlay One Image on Another
Composite two images with the same blend modes you'd get in Photoshop — multiply, screen, overlay, difference and the rest. The first file you drop is the base and sets the output size; the second is laid on top. Reorder with the arrows if you got them the wrong way round.
Drop two images here
First = base, second = overlay
Which blend mode does what
Multiply always darkens: white in the overlay disappears entirely, which makes it the mode for laying scanned line art, ink textures or a signature over a photo. Screen is the mirror image — black disappears, so it's how you add light leaks, lens flares, sparks and smoke without cutting anything out first.
Overlay, soft light and hard light darken the dark areas and lighten the light ones, so they add contrast and are the usual choice for grain, paper and grunge textures. Difference is a diagnostic rather than an aesthetic tool: identical pixels come out pure black, so anything non-black is a change — useful for spotting what moved between two renders, though Image diff is more direct for that job.
Hue, saturation, colour and luminosity transfer only that one attribute from the overlay. "Colour" over a grayscale base is the classic hand-tinting trick.
Sizing and position
The base image dictates the canvas. An overlay larger than the base gets clipped at the edges; a smaller one is placed according to the position setting with the rest of the base showing through. Use overlay scale to resize it — 50% for a watermark in a corner, 200% to make a small texture cover more ground. Stretch to fill ignores the scale and aspect ratio and forces the overlay to the base's exact dimensions, which is right for gradient maps and full-frame textures and wrong for logos.
For text or a repeating tiled mark, Watermark is purpose-built. Join images places images beside each other instead of on top.
FAQ
Which file is the base?
The first one in the list. The arrows in the file list swap the order if you need to.
Can I overlay three or more images?
Only two per pass — but the output can be fed straight back in as a new base, so any number of layers is a few passes.
Are these the same blend modes as Photoshop?
They're the CSS/Canvas compositing modes, which follow the same specification for the ones they share. Results match closely; Photoshop has a handful of extra modes that browsers don't implement.
Is transparency respected?
Yes. Transparent areas of the overlay leave the base untouched, and the output keeps the base's own alpha.
Nothing seems to happen with some modes.
Check the overlay's content: multiply with a white overlay, or screen with a black one, is a no-op by definition. Also confirm opacity isn't at 0.