The person who faked that SS made two obvious mistakes.
1) Used JPEG compression for the resulting file. This allows for the kind of detection used by fotoforensics.
2) Used Photoshop or other similar image editor to edit text in the image. This introduces a different kind of flaw, that can be easily seen with the naked eye once zoomed in.
Notice the colored pixels around most of the text? That text is rendered using subpixel rendering, a tehnique used throughout the OS to increase the apparent resolution of the font at the expense of a small but otherwise indistinguishable quality loss. Normally all the text is rendered this way, including this one.
Notice the text with no colored pixels around it? That text is rendered using an image editor which only uses classic anti-aliasing.