Any photo, signature or scan, to the exact size, format and dimensions a form asks for. The file never leaves this device.
Type the size in KB - a minimum, a maximum or both - and the pixel dimensions if the form gives them. Output comes back as JPG, PNG or PDF, and a PDF of several pages works too: every page is resized like an image.
Say what the file is: a document scan, a photo or a signature. A photo is cropped to the shape asked for and never posterised; a signature has its paper cleaned to white and its ink kept sharp.
Everything happens in your browser. The file is never uploaded.