Source scale is the scale of the data source (i.e. aerial photo or satellite image) from which data is digitized (into boundaries, roads, landcover, etc. in a GIS). Typically, this relates to the source material from which the GIS databases were created. Source material includes aerial photographs, existing maps, satellite data, and information gathered from survey instruments, such as total stations or GPS receivers. Many sources of vector data are derived from remote sensing techniques, particularly from aerial photographs.

That would hopefully be contained in the metadata. I use the word "hopefully" since many agencies still do not contain to enforce the input/collection of metadata. This information can be accessed in ArcCatalog. If this information is not available you may need to contact the data provider. Failure to acquire this information may mean using a second dataset for which reference scale has been documented. That is, objects which exist in both sets of data and where scale is known at least one of these datasets. This may still a bit qualitative in nature since some methods for the collection of data sets may be semi-automated in nature. This may mean that different parts of the data were collected different scales. 

Try to Georeference those Aerial photographs and satellite imageries by using the GPS data (Latitude and Longitude). Then in ArcGIS, scale can be added.

http://www.digital-geography.com/arcgis-tutorial-1-how-to-georeferenciate-a-map/#.VMsPqyyPPT8

http://resources.arcgis.com/en/help/main/10.1/index.html#//009t000000mn000000

this may be under "Setting layer properties"

http://resources.arcgis.com/en/help/main/10.1/index.html#//00s500000031000000

Firstly georeference or geocoded the satellite image using bilinear method with positional error should be lessthan .005 meter. Then make shape file in then make arc catloge plateform. After this proces open processedimage in arc gis. and go to lebel option and define the scale north arrow scale and thematic classification and spatial location as latitude in grided or without grided form .

I suppose your data is vector data digitized over satellite or aerial images. You shouldn't speak of scale, because in strict sense the word only applies to paper maps. When you have digital images it is better to speak of the spatial resolution (pixel size on the ground). It determines the detail you can get for the vector data. If you have access to some other georeferenced digital images for which you know the resolution (e.g. Google Earth images), you can compare the detail of your vector data with the detail you see on the image.

Basically,the scale can be retrieved from the metadata, if provided by data supplier. But if you are using the secondary data, the best way is to georeference the image with any control point obtained from very accurate sources such as GPS points. U may use the spatial adjustment from ArcGIS for this purpose.