Resize an image to 1080 x 1920

Only if your source has a different aspect ratio. 1080 by 1920 is a 9:16 frame; a source of any other shape has to be either cropped to fit or stretched. The tool keeps the ratio by default and pads or crops rather than stretching.

Making an image smaller is safe and usually looks sharper than the original. Making it larger is not: the extra pixels have to be invented by interpolation, and the result is soft. If you need a genuinely bigger image, start from the largest original you have rather than enlarging a small one.

Resizing changes the pixel dimensions of the whole image and keeps everything in frame. Cropping throws away the parts outside a selection and keeps the remaining pixels at their original size. To hit an exact size without distortion you usually crop to the right shape first, then resize.

By default yes: set one dimension and the other follows, so nothing is stretched. You can unlock it and set both independently, which will squash or stretch the picture. If you need an exact width and height from a differently shaped source, crop to that shape first.

No. Image Resizer runs entirely inside your browser using the Canvas API. The file is read from your device, processed on your device, and the result is handed straight back to you. It never travels to a server, so there is nothing for us to store, log or leak.