Why change a picture's size
Forms ask for photos in exact pixel sizes, websites need images that fit their layout, and social media looks best with certain dimensions. Resizing changes how many pixels wide and tall a picture is, which also changes its file size.
How the settings work
Choose Pixels to type a new width and/or height, or Percentage to scale the picture, for example 50% for half the size. Keep “Keep the shape” ticked so the picture is not stretched — type one side and the other is calculated for you, or type both to get exactly that size, cropped evenly from the centre. Untick it only if you prefer the whole picture squeezed or stretched to the exact size.
Pixels, KB and print size
Pixel size and file size are different things: a smaller pixel size usually means fewer KB, but a form that asks for “under 50 KB” needs a tool that checks the KB, such as Resize Image to 50KB. For printing, more pixels give sharper prints — about 300 pixels per inch is a common print quality.
Common problems and how to fix them
The picture looks stretched: turn “Keep the shape” back on, and crop to the right shape first with Crop Image. A small picture looks blurry after enlarging: resizing cannot add detail that was never there. The form rejects the photo for its KB size: use a KB-target tool after resizing.
Good habits
Crop first, then resize; keep the original full-size file; and resize several pictures together by percentage when they all need to shrink the same way.