First, identify the kind of file

Open the file as a layer above your photograph. If the corners are transparent, the layer already has an alpha channel: start with Normal. If the image is bright light against solid black, start with Screen. Read the supplied index rather than judging only by a web thumbnail, which may display transparency against black.

For this collection, light rays and luminous effects use Screen. Fog, smoke, steam and physical weather particles use transparency with Normal. Opaque portrait backgrounds belong below the cut-out subject.

Why Screen removes black

Screen combines the base and overlay so that black leaves the base unchanged and brighter values lighten it. A grey background therefore does not disappear: it creates a pale wash over the photograph. Screen is appropriate for adding light, but it cannot create a dark smoke silhouette on a bright scene.

Do not erase the black with a hard selection. That usually throws away dim light around the beam and produces a brittle edge. Keep the source layer intact and use a layer mask to remove unwanted spill.

1. Place the black-backed light effect above the photo.
2. Set the layer blend mode to Screen.
3. Position the light so its direction agrees with the scene.
4. Lower opacity and mask light away from areas it should not reach.

Why transparent smoke usually stays on Normal

The alpha channel already describes how much of the photograph should show through each part of the smoke. Normal preserves that relationship and the smoke colour. Switching a transparent smoke layer to Screen changes its tonal behaviour and can remove darker internal detail.

A PNG is not faulty because it looks different on black and white. Check whether its edge fades naturally on the actual photograph. Adjust opacity as a creative decision, rather than using a blend mode to hide every dark pixel.

If a rectangle or halo is visible

Temporarily place the overlay over a solid dark layer, then a light one. A rectangular wash on Screen points to non-black source values. A bright fringe around an alpha edge can indicate a matte contamination problem. Sharpening makes such fringes more obvious; it does not repair them.

Check the source at 100% before changing it. A local mask can remove unused edge regions, but if a halo runs through fine smoke strands, choose another file. Avoid adding blur to the entire layer just to conceal one bad edge.

Make the final check at delivery size

Inspect at 100% for edge defects and at the size the customer will see for overall strength. Keep an editable working copy with layers, then export a separate finished image. The selected blend mode should solve the compositing task, not become a rule applied to every PNG.