早期美國舊票有不少經過消戳處理後在放到網路上以新票賣出.

http://www.theswedishtiger.com/remove.html


加蓋用的油墨和銷票油墨是否類似?

Sorry, maybe that is not a good thing to talk about here. I just removed the second picture.
I highly suspected that they were altered stamps when I acquired them. I collected them to see what technique people can do currently. These two examples are the ones that are easier to spot. I guess I'm the only few collecting this kind of stuff. I posted the pictures here not to confuse peopel, just for reference.It seems to me that this topic is too sensitive, I should stop right here.

If the overprint can be wiped completely and undetectedly, that would be very scary. A fellow from APS local club told me few years ago that anything is possible now. He had seen one that he could not tell it's been altered and yet he is an expert on altered stamps.

I see your point. If I post one that even an expert can't tell, that will create a signicant panic on stamp collecting here. I appreciate your advice.

I would not worry about the flying geese without denomination being targeted. We all know how many they exist and it is highly unlikely one would show up on an online auction.

The faint denomination that I took down from the posting is an obvious one, one that the maker could have made it completely undenominated. But again, he or she knows that it would attract too much attention then get removed by Ebay.

BTW, is there a better word to describe stamps like this? They are not fake but altered. Forging stamps or money can be called counterfeiting. Not sure about this.

I remebered I read this book at the library a while a go. It's a bit old. I'll try to look for newer edition if it exists. Thanks for the info.

個人並沒集大龍票, 不過最近因大陸集郵興起,大龍票自然是問題票的焦點. Early US classic suffers the same issue here.
My job is related to test engineering, therefore I always look for evidence and proof.

在美國網路這個 topic也是相當敏感的. 若是談論偽鈔, Secret Service 恐怕馬上來敲門.

Below is a very good and yet inexpensive way to detect fraud - remember to hover your mouse on the large picture at the bottom of the page.

http://petapixel.com/2010/03/25/how-photoshop-helped-save-my-dad-from-ebay-fraud/
 
底下這個網站小弟蠻喜歡的. He is a member of the APS.

http://riversidestamps.com/Fakes.shtml

集郵有時運氣相當重要.

大約一年前在Ebay看到有人拍賣東北44加蓋. 當時有兩筆,每一筆約一百枚. 第一筆沒什麼變異, 第二筆看的出有數枚橫星(圖一右頁. 這大約是當時的解像度).就以約兩百美元標下第二筆. 收到郵票檢查後大吃一驚.

一直到現在這些郵票在這活頁上的位子還未曾動過..............................

高點貳. 張愷升在書上有提到過. 與貳分的貳相似字體.

It is unclear to me whether there was a full pane (or several panes) ever existed. BTW, there is another famous variety - the one with the "two" slightly shifted to the left. I have not seen that one on auction for a long time.

A few minutes ago, while browsing through some of my covers, I found this interesting pair.

前一天都還正常, 第二天換日期時去動到年份.

還有一些類似的封, 不過這是手上找到兩天連在一起的.