Reduce Image Size (File Size) with Attachment Control
Setting on Attachment Control and/or Control Action "Transform" which would reduce size of image to target Height (by pixel), or Width, (Both would reshape image. "Transform Image" action. Option to make thumbnail, or enum of 4 common sizes.
File Attachment would have Transform File, (type/ext aware) to Max compress, Medium Compress.

Thank you for your feedback. We are exploring a way to include new controls easily into SmartForms, which may address your request. Stay tuned for more information, and we'll update the status of this request as projects continue.
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Jeffry Belnap commented
Output of control action could target other control, or overwrite same control. (This works in iso storage where server temp holds the "uploaded file" ....