What you need is a droplet.
Droplets are drag-and-drop mini-applications — essentially applets — in macro form that can exist outside Photoshop on your desktop, on your taskbar, or within a folder. They’re always available, so you can apply them to any image files you want. Think of them as batches waiting to happen.
You just need to drag the file or files that you want to process onto the droplet. Photoshop doesn’t even have to be open at the time. When you drop the file or files, the droplet opens Photoshop and carries out the steps in the action embedded in the droplet’s instructions. You must use an existing action as the core of the droplet.
To create a droplet, follow these steps:
Choose File→Automate→Create Droplet.
The Create Droplet dialog box opens.

In the Save Droplet In area, click the Choose button and enter a name and location on your hard drive for the droplet application. (Don't worry, you will be able to select where will your processed images will save at in a further step)
The location isn’t of overriding importance because after you create the droplet, you can drag it to your desktop, a toolbar, or wherever you like.
The rest of the Create Droplet dialog box is the same as the Batch dialog box, except that you don’t have to specify a source. Droplets use the files dropped on them as their source files.
In the Play area, select the actions set, action, and options. (this is the only confusing bit if you are not used to actions, but in few words you gotta have an action previously recorded with all the steps you want your images to go through every time you drop a file on the droplet)
Select a destination from the Destination pop-up menu.
Specify any file-naming options you want.
Specify how Photoshop should process errors.
When you finish, click OK to create the droplet.
To use the droplet, just select the file, files, or folders that you want to process and drag them to the droplet applet.
Original article.
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checkbox on the PNG format options popup