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There's no limit, although you should make sure that all images will be seen within the period of your ad exposure with enough appreciation time.
How can I connect a Campaign Level Rules Engine to a Story Level Rules Engine?
After finishing your rules engines you may apply these on the drop down option in the campaign & story levels rules engine field. After which, all assigned names of context can be supplied in the drop down field of your stories to connect them with a specific rules engine. See Rules Engine for step by step instructions.