Sorry for the late reply. That looks great, I’ll be able to test it later on today.
Edit:
The image is not showing. I'm getting a green texture. After verifying code and path (setting different textures and copying the file into several folders to try) and some research, I found this silly limit that all texture file sizes have to be a power of 2. Turns out my first preference of just the bar isn't going to work unless the image is extended to 256x256 with a bunch of space and I use SetTexCoord().
So, I ended up figuring it out after all with some trial and error. I found this program called BLP Laboratory, opened the ArcheologyToast.blp file, converted to png, opened Gimp, deleted the old overlay (this took a bit, had to import as layers and found the alpha lock button), imported the png you gave in your post and moved to the old spot (kept looking for a hand tool, it's a four-point "move" tool lol), saved to the toast png, converted back into blp, and went with the second part of dropping it into Interface\ARCHEOLOGY with no supporting code.
I sincerely appreciate altering the bar for me. I originally started out, before this thread, by taking a screenshot of the bar ingame, adjusting the segments in paint, then trying to add alpha in Gimp. It just wasn't turning out as clean as you made it. I should've found that BLP program earlier.
I have attached the ArcheologyToast.blp file if anyone else wants this. Just drop the file into this path with WoW not running (watch the spelling) and you're set:
World of Warcraft\Interface\ARCHEOLOGY\ArcheologyToast.blp
