Hi sorry for the simple question.
I put a .jpg in COP now I need to control the transparency like In Photoshop Layer.
I remember that exist a node with I could enable some option and control transparency with a slide but I do not remember what node can do it.
Can you help me?

The composite COP has foreground and background weights, if that's what you mean. Also you can change the alpha channel to affect how it is composited with an over.

Are you looking for something like the Lumakey COP, which generates a matte based on the luminance of the image? Set the minimum luminance to a relatively small number like 0.01, click off “Discard Keyed Region”.

Hi Jsmack and Twod thank you very much your help are welcome.
My problem in fact is very simple.
I have an image in Comp1 in Houdini the only thing that I wish to do is control the opacity to make image transparent like any common layer in a image editor(such Photoshop)
Jsmack it is not a composition I want to do, like this I can not contro the opacity balance in a compostion because I have only one image.
Twod I tried LumakeyCOP it was near but I think not exactly it.

I know it do not help but exist a node in COP that can do it…I used to it long time ago but I can't remember.
Was a node that not need two nodes to operate I turn on an option and use a slide…I not remember what was the name or configuration.
To be more Challenging I not found the topic here on The Forum… but it exist.
I did some “Gambiarra”(this word in Brazil means - I did anything that work but not exactly the right thing)
But to make my students life easy I want to find that node.

In that case, you'll want to append a Color COP, change “Add Plane” on the Image tab to “A”, and then adjust the alpha value on the Color tab. If you want the result premultiplied, use a Premultiply COP afterwards.

Twod you are a Warrior and you Won this Battle. :-)
Thank you very much.
Only with Color COP I solved the problem.