I think what you are doing is clicking the image button and pasting the code from the sprite page into there. You don't need to do that, you just paste it straight into your post. For example
[![Scizor](https://img.pokemondb.net/sprites/black-white/normal/scizor-f.png)](http://pokemondb.net/pokedex/scizor)
Will come out as
The image button is for when you only have the URL of an image, like
https://img.pokemondb.net/sprites/black-white/normal/scizor-f.png