How to select text to put on transparent background

I usually end up retyping content on a new layer with the Type Tool.  In the end, you have better quality text in less time than it will take to extract background and artifacts from a scanned image.

If it's an image of a clipping, both the text and background are part of that image. If the background is off white, you can select what you want to use:

Then I use Levels to force the gray to white

Next I add an Effects layer and use the Blending option to for the wite to be transparent. You have to save as a png file to get transparency, and it must be a floating layer, so click the layer padlock to be sure.

Move that slider to the left until the white area goes transparent.

Then you place it on the background of your choice and flatten the file.