Well first off you're going to need the original tiles put back to search it in the ROM.
Once you have them back, go to that screen again and open the PPU Viewer.
Pause the emulator here and try to match tiles with the full image.
In the PPU Viewer you'll see the separate tiles, each one with a Unique Tile ID, simply write down the ID of the tiles and in which order they are being written in the screen from upper left to right.
For example, i'm gonna say the mountains have consecutive ID,s, search the ROM for the ID in the order from left to right per scanline:
01, 02, 03, 04, then the ones from the tip of the castle.
It's just a mwtter of knowing what each tile ID is and searching those values in the order they are in the screen in the ROMs data.