Photographs and gradients
JPEG is widely accepted and predictable for photographs. WebP can often reach a similar visual result with fewer bytes, but the receiving form must explicitly accept it.
Transparency and flat graphics
JPEG has no transparency and fills transparent pixels with a background color. PNG preserves exact alpha and sharp flat edges, while WebP can preserve alpha with a smaller file in many cases.
Inspect the failure modes
At low quality, JPEG often shows blocks and ringing around high-contrast edges. WebP may smear fine texture. Compare the regions that carry meaning rather than judging only the headline byte count.
Compatibility before compression
Government, school, and legacy business forms may list only JPG or PNG. A slightly larger accepted file is more useful than a smaller format the destination rejects.
Run a controlled comparison
Start from the same original, keep the dimensions fixed, and create one JPEG and one WebP near the same byte target. Compare them side by side at normal viewing size and at 100 percent. Look separately at faces, text, foliage, fabric, and hard edges. This avoids mistaking a smaller file for a better file when the encoder has removed detail that matters. Do not repeatedly convert an already compressed result, because each lossy generation can compound damage and makes the comparison unfair.
Plan a fallback for the receiving workflow
Before deleting either candidate, test the chosen file in the actual upload or publishing system. If WebP is rejected, return to the untouched original and create a JPEG at the required limit rather than converting the rejected WebP again. If transparency is essential, neither ordinary JPEG nor an opaque matte is equivalent to the source; use PNG or alpha-capable WebP only when the destination supports it. Keep notes about accepted formats and dimensions so later exports use the same verified constraints.