A PNG can contain a fully opaque white rectangle. Checking the filename will not tell you whether a cutout has usable transparency. Check the pixels against another surface before shipping the asset.
Reproduce the visible failure
Put the exported image in a small HTML page with a dark background. Set a fixed display width and preserve its aspect ratio. If a rectangle appears, distinguish opaque backdrop pixels from a browser layout issue. Changing the element’s background cannot erase pixels inside the file.
Inspect the preparation step
The BGRemover guide to making a transparent background covers the export workflow. Open the actual downloaded result, rather than inspecting only an editor preview.
Choose a format deliberately
MDN’s image format guide documents format capabilities, including transparency support. File format support and the presence of useful alpha data are separate checks. Converting an opaque JPEG into PNG preserves the white pixels unless another step removes them.
Add a visual acceptance check
Review the asset on light and dark surfaces at its intended size. Include gaps inside handles or lettering, where leftover pixels are easy to miss. Keep an original for corrections and export a new version when the mask changes. This small check catches failures that a successful build cannot see.
Include this inspection in the asset review notes. Record the intended surfaces and displayed width so another developer can repeat the check after a replacement file arrives.
