The relationship of texts and images can mean multiple things. They interact with each other in numerous ways.
Some word texts and pictures actually connect. The text by the image could actually be what the image is. Or it could be something that seems completely irrelevant but it may have a more meaningful connection.
Text and Image combination can also be used for some humorous purposes. Like a cartoon: the image shows the event or happening in the cartoon and underneath or around it can be the caption. The caption texts serve as dialogue or lines of what the characters are saying or a satirical comedic comment.
The word bubbles are used in cartoon like images to have a spot for the texts that the character is saying. The text actually being in the image can create more of an impact on the reader. It can keep them more focused or understand the text's meaning easier, because the character in the image that the word bubble belongs to, shows expression that helps the mood or tone of the whole combination together.
This is my summary of the relationship between texts and images.