This page contains information about common problems with Alt1 capture and how to fix them. You can change the capture settings by going to capture tab of the Atl1 settings.
Alt1 has three capture modes, OpenGL or DirectX are preferred and Desktop can be used as fallback. Alt1 will try to detect the correct capture mode but might make the wrong choice.
You can select different radio boxes to make the preview box show the game client.
Since Windows 8.1 some programs can be stretched out by Windows in order to make them larger on high DPI screens. Alt1 normally automatically detects this, but certain combinations of settings might make Alt1 make the wrong choice. You can override this click checking the "override DPI scaling detection" checkbox. Toggle this checkbox in such a way that the preview box shows the full game with no extra space around it.
If all other settings seem correct and Alt1 still can't find the home teleport button there might be a different problem.
If you have a Nvidia graphics card some graphics settings might be overridden in your driver. One of these settings breaks Alt1 as it blurs out your complete game.
There is more info on this in this thread on the RuneApps forums.