Cropping and resizing are different operations
Cropping discards the parts of the frame outside your selection and leaves the remaining pixels untouched at their original resolution. Resizing keeps the whole frame and changes how many pixels describe it. Reaching for the wrong one is why images end up stretched or unexpectedly soft.
When a photograph has to fit a specific shape, crop first and resize second. Cropping to the target aspect ratio decides what stays in frame; resizing then brings it to the pixel dimensions the destination wants, without distorting anything.
The ratios worth knowing
1:1 for profile pictures and most product listings. 4:3 is what phone cameras and older screens produce. 16:9 is video, presentation slides and hero banners. 9:16 is the vertical full-screen shape used by phone-first video and story formats.
Platforms crop automatically when your image does not match, and their automatic crop is centred and indifferent to your composition. Doing it yourself is the only way to guarantee that a face, a product or a headline survives the process.
Crop for composition, not just for fit
The strongest reason to crop is rarely the shape — it is removing everything that competes with the subject. Distracting edges, empty foreground and accidental background clutter all dilute an image, and cutting them is the fastest improvement available without an editor.
Leave a little room around the subject rather than cropping tight to it. Faces in particular need space above the head, and a subject pressed against the frame edge reads as a mistake. If the image will be used in more than one shape, crop conservatively so there is margin left for the next one.
What happens to the file
Cropping in a browser decodes the image, keeps the selected region and re-encodes it. For a PNG that is lossless and costs nothing. For a JPEG it is one further lossy generation — negligible at a sensible quality, but a reason not to crop the same file repeatedly.
Metadata is not carried through. Location, camera settings and timestamps are dropped along with the discarded pixels, which is a privacy benefit more often than a loss: a cropped screenshot or photograph leaves this page without the GPS coordinates the original was carrying.
It is worth saying what does not happen: nothing is uploaded. The crop is performed on a canvas in your own browser, so a screenshot containing account details or a photograph of a document is processed on your machine and never sent anywhere. That also means the tool keeps working with the network disconnected once the page has loaded.