I'm looking for a Photoshop expert to merge two different images and add elements to make it look realistic. Please reply with examples of what you've done in the past. Thank you.
The easiest way is using clone brush and paint it in place. Add some masking to make the edges realistically blurred as it (Nessie?..) seems to be moving fast, and use adjustment layers to match the background Hue/Saturation. Done. Good luck!
Merging two images can be done by merging layers (by pressing Ctrl+E). If your images get affected by layers merge, then merge the images by Layer Masking. Layer masking is a easy thing to do. An expert web designer can quickly and nicely do it for you.
Too bad you can't post two thumbnails of the images so we can get an idea of how well they might merge together. Some images will merge more seamlessly together than others.