URL to the first image in the subject

I'm not strong in programming. Is it possible to add a direct url to the first picture in the topic in the meta tag?

Let's say something like this:

<Meta property = "og: image" content = "{$ firstImage}" /> 

What would have happened is something like this:

<Meta property = "og: image" content = "/uploads/monthly_2017_08/12.jpg.7532595a79589bf54bec9696b828eb28.jpg" /> 

My goal is to get the picture next to the link in the telegram. Help please!.