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Unfortunately, we do not have an app that would compress or resize the uploaded files. But I will escalate this to our development team as a feature request, we will update you here in this thread if there's any progress on it. Please do take note that we cannot give an estimated date to when this will be implemented or be considered.
If you are worried on getting too much space on your JotForm account, I would advise that you take advantage of the app integration that we have for file storages and sharing. Here's that page: http://apps.jotform.com/category/file_sharing_and_storage.
You might also be interested in checking this guide on how to change the upload limit of a file: http://www.jotform.com/help/33-Changing-the-Upload-Size-Limit.
I hope that helps.