A Free Difference Overlay Reveals What AI Changed in Your Product Photo
Use Photopea’s free Difference blend mode to compare an AI-edited product image with its original and spot changed labels, engravings, clasps and edges.
An AI-edited product photo can look convincing at normal size while still containing a changed clasp, softer engraving, shifted label or altered edge. A simple side-by-side check helps, but the eye is easily distracted by the new background or lighting.
A Difference overlay gives you a stricter check. It compares the pixel values of an edited image with the approved original. Areas that match become black or very dark. Differences appear bright or coloured, making small changes easier to locate.
You can build this check in Photopea, a free browser-based editor with layers and blend modes. It is most useful after background removal, generative cleanup, local object removal or any AI edit that is supposed to leave the product itself unchanged.
When this test works well
Use the workflow when the original and edited files show the product at the same angle, scale and crop. A clean studio image and an AI background replacement are a good pair. So are an original image and a version where a stand, dust spot or unwanted prop was removed.
Do not use Difference mode to judge a newly generated angle, a virtual try-on image or a completely rebuilt lifestyle scene. Those frames contain different pixels by design, so almost the entire comparison will light up. For those jobs, use visual reference checks and verified measurements instead.
Step 1: keep the approved source untouched
Start with the highest-quality approved photograph of the real SKU. Do not compare the AI result with another AI result. The camera original or a carefully retouched master should remain the source of truth.
Make working copies with clear filenames such as “bracelet-silver-master” and “bracelet-silver-ai-background-01”. Avoid repeatedly exporting JPEG files before the comparison because each compression pass can add small pixel differences that create noise in the overlay.
Step 2: place both files in one Photopea document
Open the original in Photopea with File, Open. Then drag the edited file into the open document, or use File, Open and Place. Photopea’s documentation says that dropping a file into an existing document inserts it as a new Smart Object layer.
In the Layers panel, put the edited image above the original and rename both layers. The two files must have the same pixel dimensions and alignment. If they already came from the same source and the AI tool preserved the canvas, they may line up immediately.
Step 3: align before judging
Select the top layer and lower its opacity to about 50 per cent. Look for doubled product edges. If the edited image moved or resized the frame, use the Move tool and Free Transform to align the product with the original.
Use hard, recognisable anchors: the corner of a label, the centre of a stone, a screw, a clasp or the end of a box. Do not align only by the background because the background may be the part that changed.
If the AI altered the product scale or perspective, stop and record that as a failure. Transforming the comparison layer until it fits may hide the very distortion you need to catch. Alignment should correct an accidental canvas offset, not rescue changed product geometry.
Step 4: switch the edited layer to Difference
Return the top layer to 100 per cent opacity. At the top of the Layers panel, change its blend mode from Normal to Difference. Photopea supports blend modes and opacity on selected layers.
Difference mode mathematically compares the active layer with the layer below. Identical pixels produce zero difference and appear black. Brighter marks show where colour or brightness values do not match.
Do not expect the entire background to stay black after a background edit. The useful question is what happens over the product. Zoom to 100 per cent and inspect the regions that customers rely on.
Step 5: read the pattern, not just the brightness
A thin double outline around the product can indicate a position, scale or shape shift. Bright marks on engraving may mean letters were softened or rewritten. A changed pattern around a jewellery clasp, stone prong, bottle cap or printed logo deserves direct comparison with the master.
An even glow across the whole product often means colour, exposure or contrast changed globally. That may be intentional during relighting, but it still needs checking if accurate metal colour, fabric tone or packaging colour matters.
Fine speckling across the full frame can come from JPEG compression, sharpening or resampling. It is less concerning than a structured new edge, missing line or changed character. Toggle the top layer between Difference and Normal, and also try 50 per cent opacity, to understand what the bright pattern represents.
A product-detail checklist
For jewellery, inspect the outer silhouette, chain path, number and position of stones, prongs, clasp, jump rings, engraving, hallmarks and polished edges. Compare metal colour in Normal mode after checking geometry in Difference mode.
For packaged products, inspect the logo, label text, quantity, cap, pump, seal, barcode area and the exact boundary of transparent or reflective packaging. For clothing and accessories, check stitching, fasteners, printed motifs and the shape of openings or straps.
If a critical detail changed, return to the approved master. Re-run the AI edit with a tighter mask, or composite the untouched product pixels back over the generated background. Do not use another broad AI pass to repair an AI-created product error.
Save the comparison as part of the workflow
Save the layered file as PSD so the original, edited layer, alignment and blend mode remain available. Photopea uses PSD as its main layered format. You can also add a short text layer noting the date, tool and pass or fail result.
For a catalogue team, keep the approved master, final image and QA file together. That creates a simple record of which version was checked instead of relying on someone remembering that an image looked fine in a thumbnail.
What a Difference overlay cannot prove
The overlay can show pixel changes. It cannot prove that the original photograph is accurate, that a gemstone is genuine, that a colour matches the physical item under every screen profile or that a size claim is correct.
It also becomes noisy when files have different compression, colour profiles, crops or resolution. Treat it as a fast diagnostic tool, then confirm suspicious areas in Normal mode against the real product and its verified specifications.
The useful habit
Run the overlay whenever an AI tool claims to have changed only the background or one local area. The check takes a few minutes, costs nothing and turns vague confidence into a visible comparison.
AI can make product-image production faster. A Difference layer helps make sure the speed came from changing the presentation, not quietly changing what the customer will receive.
Sources
Photopea, “Layers,” reviewed 3 October 2026: https://www.photopea.com/learn/index.php?page=layers
Photopea, “Opening and Saving Files,” reviewed 3 October 2026: https://www.photopea.com/learn/opening-saving
Photopea, “Free Online Photo Editor,” reviewed 3 October 2026: https://www.photopea.com/
Adobe, “Blending Mode Descriptions,” reviewed 3 October 2026: https://helpx.adobe.com/ca/photoshop/desktop/repair-retouch/adjust-light-tone/blending-mode-descriptions.html