Match the destination
Use JPG for ordinary opaque photos when broad compatibility matters. Use PNG for crisp interface screenshots, diagrams or lossless decoded pixels. Use WebP when the receiving system accepts it and its compression is useful. Verify the target application first; the smallest output is not useful if the recipient cannot open it.
Decide what alpha should do
Transparent areas can stay transparent in PNG and WebP. JPEG has no alpha channel, so Keep alpha uses white for JPEG. Choose white or black deliberately when a flat background is needed. Check partially transparent edges against the intended background instead of assuming that one preview background tells the whole story.
Convert a representative batch
Select up to twenty static JPG, PNG or WebP images. The tool bounds both compressed bytes and decoded pixel counts. Choose JPEG / WebP quality; PNG ignores that lossy-quality choice. Review dimensions and before/after sizes for each result. Numbered file names distinguish originals with the same base name, and the ZIP contains every accepted image.
Inspect the downloaded result
Open one photograph, one image with fine text and one transparent image from the ZIP. Compare orientation, edges and backgrounds. Metadata is not copied, but visible private details still remain in the pixels. Conversion cannot recover details already lost through compression. Keep original files until the destination has accepted the new copies.