Want to pimp out your deck with promos, but aren't quite ready to subscribe yet? I have an answer for you.
Attached is an alphabetized list of all Magic: the Gathering sets I currently have installed (anything and everything on the official OCTGN MTG page), along with their corresponding folder names in the Image Database.
To change an image:
1. Download the attached txt file.
2. Look up the card you wish to change and find a (NON-promo) set in which it was printed. I recommend magiccards.info for this, as they often have the promo images right on their site as well as the regular ones, unlike Gatherer.
3. Find the set in the txt file, and copy the corresponding GUID.
4. Navigate to the "Image Database" folder within your OCTGN data directory, then paste the GUID into the search bar.
5. Inside the set folder, browse until you find the card you want to change. Leave the folder open.
6. Find the alternate image you want online, and download it to the set folder.
7. Rename the original image, but copy the original name first. Then paste the original name into the new image's rename box.
8. Done! In order to view your updated images, you will probably have to restart OCTGN, as it caches images to run faster.
A few last notes:
-The Pre-M10 Core Sets are listed under their official names. Alpha and Beta are in the "L"s, and 7th Edition is in the "S"s, etc.
-Sadly, the following sets were not in my database: MTGO Masters Edition IV, Anthologies, From the Vault: 20, and Duel Decks: Jace vs. Vraska. Please forgive these omissions; I will update the document as I acquire new images.