I use Ditto for this for images to be posted on the web. Once you create a template, it's a one click process to do this from within Bridge.
One of my templates adds borders and shading to create a frame and then applies my logo anchored to the lower right corner that is sized according to a percentage of the image. I have created another template to do the same thing but apply the logo to the lower left corner instead. You can add effects to the logo including adjusting the transparency. This is assuming that you have already created a logo with a transparent background as described above.
Here's an example:
Norma