Photo by Hendo Wang. 
IDEFICS accepts text and image prompts. However, to caption an image, you do not have to provide a text prompt to the 
model, only the preprocessed input image. Without a text prompt, the model will start generating text from the 
BOS (beginning-of-sequence) token thus creating a caption.
As image input to the model, you can use either an image object (PIL.Image) or a url from which the image can be retrieved.