How a photo becomes exactly 2MB
108pdf first saves your photo at maximum JPG quality, which already makes most small files larger. The remaining bytes are added as JPEG comment data, a standard part of the format that viewers and upload portals ignore. The picture you see does not change, and the file is exactly 2MB.
Some forms ask for a scan of at least 2MB, or a high resolution image. Turn on "Also enlarge dimensions" if the portal also checks width and height.