Worthy Of Sending For Cert?

If it is not what will it cost you? Worth a try.

The comparison stamp template is not from the same issue of the stamp that you are comparing it against.
Simply stated, a U.S. Scott 613 stamp is a U.S. Scott 612 stamp with the gauge of perforation of a U.S. 610 stamp.
Thus, having a known U.S. Scott 612 and having a known U.S. Scott 610 can be helpful in identifying a U.S. Scott 613 stamp.

Images too small and template useless to tell anything.

I have a 610 and a 612. Let me get better images. I'm wanting to look at this "bad boy" from every angle possible, with y'all's input #129310;
Of note, there are no ink dots on the back. Thanks and will return
Kara

So… I should cut the corners off of the flat plate perf 11 stamp and use it for the template? Duh?

And some sick bastard actually wrote "613" on the back of the stamp in the middle right. Be my luck to cut the corners off of a real 613!!
Kara

Ok, let's come back to reality and common sense.
If you are going to make a template, select a used stamp from this series, with contrasting color, like a 1 or 2 cent of which you are confident in the identification and printing method.

Otherwise, it should be fairly easy to overlay intact stamps from the above selection to demonstrate the height comparisons of the printed images.

Kollectomaniac as a brand-new member are you seeking advice or putting out toxicity?

No no, my intention was only to get help to feel confident about my stamp. Innately, Stamps cannot be a "toxic" topic

You guys are worse than nurses! You eat your young

If you use the search bottom at the top and enter 'scott 613' or 'harding' you will get an idea of how many times someone thinks he or she has this stamp. When people are informed they are not going about it in the correct manner the poster becomes abusive. None of these posters ever have returned, not even to show how wrong everyone had been.

Very experienced people have given you good information. Take John Becker's advice.
Post a scan or a picture taken with a stabilised camera, not with a device held in hand.

It is great that you have a 610 (flat plate) stamp identified and two 612 (rotary press) stamps identified to compare your bottom stamp against.

Compare the height (vertical design frame length) of your subject stamp against the height (vertical design frame lengths) of the rotary press stamps.

A 613 stamp should have at least the same height (vertical design frame length) as a 612 stamp.

It would be great if the Scott catalogue could explain that the 613 rotary press variety is a 612 stamp with perf. 11 gauge flat plate stamp perforations instead of the regular perf. 10 gauge rotary press stamp perforations.

So… I'm 90% confident that I could very well have a Scott 613. I've checked my 1923 2c black Harding stamp against all ways that I know: Perf 11, longer than a flat-plate template laid on top of it, no ink dots on the back. Are there other "inspections" that could pass it? The result of my poll is to PAY to have the stamp authenticated. The previous forum discussion on "choosing an Expertizing company/person" helped. Thank you for your posts and information.

I think you have done a reasonable job of trying to identify it and you would always wonder about it if you did not have it certified. Send it to the Philatelic Foundation; if it is not a 613 you will only be charged the much smaller fee for what it actually is and if it is a 613 you won't mind paying the large fee! Just my two cents; I tried to vote "yes" in your poll but it would not take my vote. Said I had already voted which I had not.