This dialog sets how RansenScan recognises small photographs within bigger scans.
You can find this under Tools menu, Auto Recog Config item. It is not too complicated, but if you have any doubts click on the Set all to default button and then on OK.
The minimum size slider says "any objects less than this size will not be considered as photographs to extract from the larger image." You are shown the size in inches and in centimeters.
The maximum size slider says "any objects larger than this size will not be considered as photographs to extrcact from the larger image". You are shown the size in inches and in centimeters.
To get an idea of the sizes of your photographs you can see the percentage values under the preview in the sub image fine tuning dialog. For example in this case the image is 17.7% by 23.8%:
The max aspect ratio slider sets how thin or tall an image can be and still be considered a photograph. It is simply the width of an image divided by its height, or vice versa depening on how you want to look at it!
Most photographs are within a value of 2, so 2 is a good setting to use. You can find out exactly what aspect ratio sub images are by using the sub image fine tuning dialog image size information. For example in this case the aspect ratio is 1.4:
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The aspect ratio is the largest dimension divided by the smallest dimension.
All of these things help RansenScan avoid classifying small objects inside photographs as photographs themselves, or as classifying two touching (in the phsyical not emotional sense) photographs as a single photograph (emotionally touching or not).
Unless you are scanning very strange objects the default settings should work best.
Remember that if you want automatic recognition to work when you lay your photos on the scanner you must follow these rules, look at these examples too.