: You can achieve it by creating an Action that then can be used in a batch operation. The following is a summarized step by step description on how to achieve it in case you already

You can achieve it by creating an Action that then can be used in a batch operation.

The following is a summarized step by step description on how to achieve it in case you already know your way around Photoshop. See further down for detailed description on how to do it:

Open a representable image for recording an action
Create an action and start recording
Flatten the image, make transparency by using magic wand on pixel 0,0, invert the selection and add mask.
Stop recording
Close the image, without saving any changes
Use File->Scripts->'Image Processor' to run the new action on all files, and export them as TIFF. Do not use JPEG as it does not have an alpha channel.
Done!

Detailed step by step:

1. Open a representable image

Go to File->Open, pick one of your images that is representable for the other images, and open it..
Create a new empty layer (used for later to enable 'Flatten image' option)

2. Create action and record

Locate the Actions panel, ensure that it's visible by making sure Window->Actions is checked.
Click the Create new action button (see image below)
Let's call it 'Transparency Action' for the sake of ease.
Click the Record button to start recording

3. Apply image transparency

In the menu, go to Layer->'Flatten Image'.
Right click the (only) layer and select Convert to Smart Object
Zoom in on the upper left pixel so you easily can click it with the Magic Wand
Activate the Magic Wand Tool
At the top of the screen, under the menus, set the desired Tolerance (If unsure set to 0)
Click on the upper left pixel with it
Press Select->Inverse
Add a layer mask by pressing the Add layer mask in the Layer panel. (See image below)

4. Stop recording

Press the Stop recording button in the Actions panel. The action is now made.

5. Close the image

You can close the image and you do not need to save the changes.

6. Batch process

Goto File->Scripts->'Image Processor'
Select the source and destination folder. Check the Include sub folders and Keep folder structure if that is something you want.
Make sure only the Save as TIFF is checked, JPEG cannot be used as it does not have an alpha channel.
Check the Run Action and pick your 'Transparency Action'
Click Run and go take a coffee..

7. Done!

That's about it. Hope everything makes sense and that the solution fits your problem, although your question were posed a long time ago...