Resize image

No. Each picture is decoded, drawn at the new size on a canvas inside this page, and encoded again — all in your browser. Nothing is sent over the network, so no copy exists anywhere else.

“Longest side” is the safest for a mixed batch: it fits both portrait and landscape pictures inside the same limit without squashing anything. Use width or height when a layout needs one exact dimension, percentage to shrink everything by the same amount, and exact size only when you accept that the picture may be stretched.

No. Enlarging only spreads the pixels you already have over a bigger area, so the result looks soft. Leave “never enlarge” switched on unless you specifically need the larger canvas.