As its self explanatory name suggests, an Anchor is a position keeper. It plays an essential part in warping images that will be uploaded in the future to match the master form, before extraction can properly take place.
Thus, anchoring properly is extremely important to yield favorable data extraction results. Identical parts among your documents make good Anchors. It's also recommended to have at least two Anchors, preferably stretched as much as possible on the master image.
If you have only two Anchors, their location should be any of the following, to boost accuracy: top and bottom; top left and bottom right; top right and bottom left; or left and right. The idea is to cover as much area as possible with the longest distance possible between the Anchors.
When you are unsatisfied with the extraction accuracy and it appears to be related image warping, try adding more valid Anchors. Areas that show up in every single document under the specific type of your form make a valid Anchor.
The screenshot above is an example of Anchor. The right bar has a check box that allows users to decide whether one is enabled or not. Two Anchors are marked here, where the selected one is the title of a Business Registration form and the other top left one with the word "ORIGINAL" in it.
As mentioned above, to boost image warping accuracy which improves that of data extraction, Anchors should be spread across the master form as much as possible, which is indicated by the green box in the below image. We have marked only three here for simplicity where the our actual Business Registration form template has much more Anchors.