Skillcapes will raise the level of the skill temporarily to 100, and will give the bonus to the skill, such as with the Strength cape, you can hit higher. While doing the Prayer or Hitpoints cape emote the level can't be raised to 100, but if you are down in that skill it can be raised up to 99, 1 level every minute. You can raise it the level by taking off and putting on the cape, or going into the equipment interface and clicking "Boost". The emote's picture is a player with a Ranging cape and Ranging equipment, even though you might not get a Ranging cape.