The maximum size for a digital photo uploaded to the Insiders is 2 megabytes (MB).
To re-size your digital photos, choose a re-sizing tool from your computer software or an online source. Any image or photo editing program will let you do this.
The basic principle is the same: open, resize, and save.
To make the image files as small as possible, they need to be saved in the right file format. The most common recommended formats are JPG and PNG.
JPG files, which are the default file format used by most digital cameras, are ideal for full-color images. This format has the best ratio between size and image quality.
PNG files support true color (+ transparency) and are saved without any loss of information.
For most resized pictures, the best format will be JPG.