I'm planning on using a slogan that I could trademark and was wondering if using the acronym "JPEG" is possible? I want to reference the fileformat .jpeg not the joint comittee it's short for. I'm thinking that the fileformat is a universally known thing but is it possible still land in hot water? I'm thinking about using ".jpeg" including the dot and in lower case.
I'm guessing that this will still be trouble. Whether the file format is universally known does not affect the validity of a trademark (if anything, the trademark is strengthened).
Trademarks serve to identify origin, and trademark owners can enforce their trademark. In brief, if an average consumer may confuse an unauthorized use of the mark as originating from the owners, it is an infringement. Usually this requires that the unauthorized use occurs within the same industry, unless the trademark is very well-known.
Note that simple reference is fine, those are generally not confused as originating from the trademark owners. However, you want to trademark your very reference to ".jpeg". This may cause problems, as it is identifiable with JPEG, the Joint Photographic Experts Group. The slogan may be confused as originating from them and they likely have the ability to enforce trademark rights. That's my take anyway, if you choose to continue down this path, you should consult a lawyer.