Does Google index text in images for search
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I need to avoid finding files in a Google Site search, so I named them in a way that they wouldn't come up when looking for information on the site. 

However, I noticed that image files, that contain some text started coming up when searching for words that exist in the text. Is it possible that search indexes the text in images or am I looking at something else?

If it does index text in images, is there any way I can avoid this or disable it altogether?

Thanks