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How does Facebook detect images when adding a link?

Answer 1

A:

I am not familiar with the way Facebook did it, but I can tell you how I would do it.

Establish web request to desired url
Parse resulted web response with regular expression, that looks for <img src="" />

Boris Modylevsky 2010-05-17 07:20:11

@Borid Modylevsky: Yes I know how I would do it to. But obviously Facebook is doing something else :)

Edelcom 2010-05-17 07:23:53

I think it uses some kind of heuristic to determine which images to show. I am not sure but compare the images on the two pages to find out whats common.

Salman A 2010-05-17 07:35:28

I always assumed it had looked for the biggest image in the page, but sounds like it is more complicated than that.

rikh 2010-05-17 07:50:12

@rikh: Yes it's more complicated. If you look at the two pages, both are functionally the same (with the same small images at the right of the page). The only difference is the 'main' text area (with the logo at the top) and with a table if data is present in the database. The same pictures which are not used by FB when using the first page, ARE displayed by FB when inserting the second page. So it has nothting to do with image size or image position, so I am at a loss at the moment.

Edelcom 2010-05-17 09:35:05

@Salman A: Did that, the images are exactly the same (except when displaying the additional logo image in the 'main' text area).

Edelcom 2010-05-17 09:35:56

Could it be trying to detect the "main content area" of the page by looking for divs with id like "content" etc, or discarding areas described as menus, nav, headers, footers etc. Then picking the first or biggest image in the content part of the page.

rikh 2010-05-17 12:05:10

@rikh: Maybe, but the two pages are functionally the same, so if it should discard something like nav, headers and the like, it should do it on both pages. I find it strange ...

Edelcom 2010-05-17 15:38:01

Answer 2

A:

My guess, is that FB hides repeated images - 'couse a repeated image normally indicates a design-element (not content). When you post a link, only images related to that articles content, are relevant.

So; make sure your image only appears once, and see if it helps!

qualbeen 2010-05-18 22:48:50

@qualbeen: I also thought in that direction. But the two pages are basically the same. What's more, the page that works has the main image repeated more than once, while the page that doesn't work has the main image only once in the text area.

Edelcom 2010-05-19 08:08:32

Answer 3

+1 A:

This looks like a duplicate of: http://stackoverflow.com/questions/1079599/facebook-post-link-image

Use <link rel="image_src" href="abs_url_of_your_image">

thomask 2010-05-19 07:47:48

@thomask: Thanks for pointing this out. Had looked for a similar question before asking mine, but used the wrong words to search for (obviously). I will try the technique mentioned there and let you know the result).

Edelcom 2010-05-19 08:13:20

Waiting patiently on results and acceptance :)

thomask 2010-05-28 17:49:11

@thomask Accepted, cause you were the first to point out the rel="iamge_src", thx.

Edelcom 2010-06-03 11:09:50

Answer 4

+1 A:

Just found this, that Facebook publishes to show how to get a specific image / video etc to appear in the thumbnail...

http://wiki.developers.facebook.com/index.php/Facebook_Share/Specifying_Meta_Tags

rikh 2010-05-24 12:47:05

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How does Facebook detect images when adding a link?

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