Encouraging a sense of scale in photos

My question relates to photographs of scat, specifically of bears. I’m a retired research scientist who studied American black bears for many years. Being fairly new to iNaturalist, I thought I could contribute by reviewing the many past observations that are only bear scat. The problem I’m having is that most photos don’t provide any suggestion of scale. For quite a few photos, I’m confident the scat is American black bear (location, apparent size, contents), but many could be confused with other species given lack of information on size. Is there a way to encourage people to add something for scale to their photos?


The getting started pages include a video tutorial called “How to Take Identifiable Photos”, but the three tips are: get closer, shoot multiple angles, and take photos that are sharp and in focus. Maybe the video could add “give a sense of scale” or something like that? I don’t know if @tiwane would be open to adding more to the video though, sometimes it’s better to keep it simple.

There’s also a discussion going on how to take photos of particular taxa, but I’m not sure how wide of an audience that’s reaching and scat isn’t exactly taxon specific.

I occasionally ID skeletal remains, and measurements are sometimes the only way to distinguish between similar taxa. On a case-by-case basis, I ask the observer to please try to include a scale in skeleton photos. Sometimes they still have access to the skeleton and can even go back and add photos. Sometimes you just have to accept that a species ID is impossible.


I don’t know what is the best way to ask people to do this, but I am all in favor of encouraging people to add a scale object in one of the photos they make for any observation where there is potential ambiguity about size.

It is often fairly simple, in one photo, to show your fingertip, finger, hand, or foot, or to put a key, pencil or pen in the shot. Some people use a coin for this purpose, but unless you also state how wide the coin is in mm, that is not a helpful scale object for someone in another country where the coins are different.

A small plastic ruler fits in a pocket or bag very easily, as does a forensic photo scale.


Wikipedia has specifications for most coins, and they’re all the same size (unlike fingers, hands, shoes, keys, pencils, and pens) so putting a coin in the shot is actually quite useful.

United States: https://en.wikipedia.org/wiki/Coins_of_the_United_States_dollar#Coins_in_circulation
Canada: https://en.wikipedia.org/wiki/Coins_of_the_Canadian_dollar#Specifications
New Zealand: https://en.wikipedia.org/wiki/Coins_of_the_New_Zealand_dollar#Current_coinage
South Africa: https://en.wikipedia.org/wiki/Coins_of_the_South_African_rand
United Kingdom: https://en.wikipedia.org/wiki/Coins_of_the_pound_sterling#Dimensions

Re bear scat: sometimes the best you can do is examine the pebbles or vegetation in the shot to attempt to guess the scale.


I have been thinking about that, but the problem in my case is that I use to take quick photos of alive bugs (or animals), and they usually don’t want to be freeze an waiting for a scale or my hand. And about bugs, if I take a wide angle, it’s no easy to appreciate the small buddy.

Anyway I’ll try to make more than one picture if possible with a general angle to help the investigation


For people who are mentally good with estimating length in mm, you can write in the Description section roughly how big the organism was – that is certainly better than nothing.

This will likely depend on the location where you find your subjects, but one idea is to identify a noticeable part of the ‘backdrop’ and measure that after the bug has left. Things like pebbles on a gravel path that are also in the photo, markings on railings, leaves that the bug was resting on, etc.

This is obviously going to be much harder to accomplish when the observation photos are tightly-framed macro shots but I thought it wouldn’t hurt to make the suggestion for those times when it might be applicable.

Coins can be useful as scale objects yes, I don’t doubt that. But your list of Wikipedia coin articles only covers the major countries of the English-speaking “Western World”.

Plenty of other articles here: https://en.wikipedia.org/wiki/Category:Coins_by_country

I’ve seen a lot of examples from iNaturalist trainings and almost all of them include use of a scale figure in their instructions.

Leaving comments and tips for improvement will help pass along best practices.

Probably the best way to encourage them would be to ID it to Ursus or Carnivora, whatever you think appropriate, and comment that without some idea about size, you couldn’t help further.

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I saw a slide talk many years ago which had photos of neotropical herps. One pic was of a remarkably large species of frog and a lens cap was included for scale (the frog was much larger). Someone in the audience asked “is that a frisbee?”

In short, you can’t beat using a ruler (preferably metric) if scale is important.

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Wow, I think that video was made just before the 2016 NPS Centennial Bioblitz, quick and dirty. I’d be happy to redo the video (I think I’ve gotten better since then), just not sure when I’ll get around to it, considering it took me way too long to get this video out and there are two more in the pipeline. Should be pretty simple, though.

It’s possible we could also include some sort of encouragement to use scale in the future onboarding revamp I’d like to do. But I think comments encouraging people to use scale in the future is likely the most effective thing to do. I would not want to overwhelm new users.

I have two friends who tattooed dots on the right side of their left index fingers, each dot is 1 cm apart. That’s another possibility…


That should be in the https://forum.inaturalist.org/t/you-know-youre-seriously-into-inat-when/1992 thread!


And I thought I would never get a tattoo. That’s awesome!

Unfortunately neither are hardcore iNat users, although they post from time to time. I’m also curious how accurate those measurements will remain as one ages.

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Fingers don’t really change much unless lots of extra weight. But as an old person I can guarantee from personal experience that those same measurements on other body parts could end up as meter marks. Just sayin…


This may also be subject to change over a long span of time, but I’ve taken to including my thumbnail when I need a quick and dirty scale reference. At 13mm across the cuticle it’s not a terribly “regular” reference length, but it works well enough and it’s cheaper than a tattoo.


I’m often frustrated by the lack of a scale in photos, too. However, I also remember a discussion here about the way annotations to a photo (such as a circle or arrow to indicate the organism of interest) were discouraged because they can affect the CV learning process. Is there a risk that the inclusion of a coin / lens cap / spotted finger / thumbnail / scale ruler in a photo could do the same? I would hope the benefit of including a scale would outweigh that, but who knows.


and that will work for the rest of us too if you mention “13mm across the cuticle” in the description. (Funny, my left thumb is 13mm and the right one is 15mm)

I carry a forensic scale and a ruler but they often are forgotten about in the moment. I’m better at remembering to use the scale on sedentary things. Many things jump or fly away so …

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I would think adding scale is more important than worrying about the computer vision training, but I can check with our vision folks. I think it’s different than adding graphics to the image.

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