Cropping decides which pixels enter the output; encoding decides how the new file stores them. CropFrame exports through the browser Canvas encoder. The preview and download use the same Blob, but that Blob is not a byte-preserving slice of the source file.
Transparency separates PNG and JPEG
PNG preserves Canvas alpha and is a reliable choice for UI assets and transparent edges. WebP may preserve alpha with a smaller lossy or lossless-style encoding chosen by the browser. JPEG has no alpha: CropFrame first fills the output with the selected matte, white by default, then draws the crop over it.
A new file means new encoding
Canvas export does not deliberately carry EXIF, XMP, ICC, comments, source DPI or camera fields into the result. JPEG and WebP quality changes compression and exact bytes. Compare the generated image visually in its destination and keep the original when metadata or provenance matters.
Keep the crop in its proper scope
CropFrame creates a new Canvas-decoded image and does not preserve metadata, provenance, measurements or evidentiary fidelity. Use it for ordinary digital publishing and design. Do not use it to prepare identity, medical, legal, inspection, emergency, navigation or other safety-critical imagery, and independently verify every important result.