Upload forms are often precise about dimensions and reject anything that misses, even by a pixel.
Read the destination's required width and height and crop to that ratio before forcing both numbers. Check the saved dimensions and any separate file-size limit. A matching pixel count does not guarantee that the subject or background meets the form's requirements.
Locked resizing keeps each image's proportions. Fixed dimensions can stretch images; crop to the required ratio first.
The encoder creates a new file. Upscaling cannot recover detail that the original did not contain.
If you need a width and height that are a different shape from your picture, forcing both would stretch it. The better way is to crop it to the right shape first with Crop & rotate, and then resize it to the exact pixel size. That keeps the proportions natural.
The presets cover the sizes people ask for most: passport, visa, Full HD, a social square and a story. The size you set is applied to every image in the batch, so a folder of pictures can be brought to the same width in one go.
No. Check dimensions here, then use Compress to a size if the destination separately limits file size.
What can be opened depends on your browser. JPG, PNG and WebP always work, and a file of another type may need to be saved as one of those in another program first.
Yes. Add them all, set the width, keep the original shape on, and each picture comes out at that width with its own height.