If art contains any stock graphics - i.e. images which have either been purchased or downloaded from other sources... technically it will never be a logo in strictest terms, because you don't own the rights to the image(s). If you don't own the rights, you can't technically claim the rights and therefore call it a "logo" in the strictest sense. "Logos" customarily contain 100% original artwork, not composites of artwork owned by others. Of course, you can purchase unlimited rights to stock art, in which case, you would own the rights and therefore could legally claim the artwork as a "logo" or trademark.
You should also be aware that most (if not all) royalty free stock services expressly state that no image may used as a logo or trademark in part or whole. You may want to read the license agreement for wherever you got the stock images.
Wikipedia defines a logo as....
a graphic mark, emblem, or symbol commonly used by commercial enterprises, organizations and even individuals to aid and promote instant public recognition. Logos are either purely graphic (symbols/icons) or are composed of the name of the organization (a logotype or wordmark).
Your described usage would certainly fall under the technical umbrella of a Logo to me... the fact that you do not own the rights means you may be in violation of any stock image service agreements and may be liable for misrepresenting artwork as original when it is not. The safest bet is always "start from scratch" if the intent is an actual Logo.
Now, that being posted... you can call anything a "logo" in general terms. It's only when you try and copyright, trademark, or prevent anyone else from using the artwork that my initial paragraph here matters. Or when someone else realizes you've used their artwork in an unlicensed manner.