Begin by piercing the needle through the fabric from back to front, near the + on the pixel leaving a six-inch thread tail at the back. Then affix the pixel to the fabric by piercing the needle down through the hole marked + and through to the back of the fabric. Repeat to make a few stitches around the pixel's + connection.
Stitch back over to your thread tail at the back and tie the two threads in a double knot.
Seal the knot from springing loose with some clear nail polish or other adhesive.
Snip the thread tails short.