Here is something based on `FilterRules` and using your post of Exif metadata format.

**FilterRules**

    FilterRules["Exif" /. (MetaInformation /. Options[i, MetaInformation]), "XResolution"]
>{"XResolution" -> 300}

There may be more elegant ways to extract the rules which form part of `MetaInformation`, I await them with interest.

This unpacks nested sets of rules:

    FilterRules[ Options[i, MetaInformation] //. {_ -> z_} -> z, "XResolution"]

>{"XResolution" -> 300}

**OptionValue**

Here is an interesting alternative which does require some knowledge of the structure of the `MetaInformation` but is otherwise nicely concise.


    OptionValue[Options[i, MetaInformation], MetaInformation -> "Exif" -> "XResolution"]

>300