Choosing a crop, and applying it to more than one photo
A crop is two decisions wearing one name: what shape the result should be, and which part of the picture survives. The controls separate them, because in practice the shape is usually imposed on you and the part is yours to choose.
When the shape is decided for you
Most crops start with a requirement. A marketplace wants square thumbnails. A video platform wants 16:9. A slide template has a fixed image well. Picking that ratio first and then moving the box inside it is far quicker than cropping freehand and discovering afterwards that the result is 3 px off square.
With a ratio locked, dragging any corner keeps the shape and dragging inside the box moves it. The rule-of-thirds overlay is there for the second decision — the intersections are a reasonable default place to put a face or a horizon when you have no stronger reason.
When it is not
Leave the ratio on Free and the box is an ordinary rectangle. This is the right mode for trimming a screenshot down to the part that matters, cutting whitespace off a scan, or pulling one item out of a photograph of several. There is no destination spec to satisfy, so the only thing that matters is what you want to keep.
Cropping a batch
Hand-drawn boxes do not generalise: a rectangle that frames the subject in one photo will cut through it in the next. Center-crop every file exists for the case where that does not matter — a set of product shots on a white background, scans from a document feeder, frames pulled from the same video. Each image is cut from its own centre to the ratio you picked, so files of different sizes and orientations all come out in the same shape.
For anything where the subject moves around the frame, crop the images individually. The queue keeps your place, and the settings stay attached to each file.
A note about rotation
Rotate and flip are applied before the crop, which is the order you want when a photo came in sideways: straighten first, then decide the framing on the picture as it will actually be seen. Rotation in 90-degree steps only rearranges whole pixels, so nothing is resampled and nothing is lost.