The shape most frames expect
4:3 is the shape of a classic camera sensor and most print sizes near it. A photo cropped to some other ratio won't sit in a 4:3 frame without bars or a trim. This grows the short side to 4:3 and builds the new strip, so the picture fits with nothing lost.
Questions
Does my photo get uploaded?
No. The picture is read, grown and encoded by code running in this browser tab. It is never sent to a server — there is no server to send it to. The only download that ever happens is the optional edge-painter model, which travels one way, from our model file server to you.
Will it change the part I already have?
No. The original is kept exactly and only the new strip is built to reach 4:3.
Can it do other print shapes?
Yes — switch the shape chip to 3:2 for 4×6 prints, or 1:1 for a square.