There are several AI art tools available that can be used to combine multiple images into a single image. Some of the best options include Image Mixer, Fotor, and DALLE-2. Image Mixer, developed by Lambda Labs, allows users to blend and combine images, as well as text prompts, to generate new and unique images. Fotor, on the other hand, uses a model called Photo Stitching to combine images together, allowing users to create panoramic and collage images by stitching different photos together. DALLE-2, developed by OpenAI, is known for its ability to generate high-resolution realistic images from textual descriptions.