Not sure if you are being sarcastic, because if you are not I think you are mistaken as I can definitely see Audience members being confused about Spider-man just showing up and thinking it must be connected to the ASM movies. If he appears to be pre-established in the MCU, audience members are going to look to whatever source may have pre-established him, and recently that would be the ASM movies. Spider-man needs his origin even if it is done quickly in the opening credits or something, but to neglect it would be a terrible idea. It is for that reason that I don't feel Spider-man can show up in Civil War as a costumed hero, unless it is done similar to what I posted earlier. However, if done that way it does venture a little into making Captain America Civil War into feeling a little like Spider-Man Civil war, but that would perhaps be part of the compromise that would need to be made in order to get a full blown Spider-man into the Civil War movie. At least that is my opinion. Otherwise, I say keep it with Peter Parker photographer until the end credits where he gets bit by the spider. Then in his solo movie have him start with his origin during the opening credits and movie on into a new story by the time the opening credits stop rolling.
Surfer