Allow user to download image

I want to allow the logged in user (if present in a specific group) to download a resized version of the image shown in a collection entry. The Asset folder has a User field data (users_pictured). So my code for the entry post is:

<Some HTML code>
{{ asset:photos}}
<img src="{{ url }}" alt="{{ filename }}" />

{{ user:in group="allowed" }}

{{ user }}
{{ if (users_pictured | in_array:89d4bffe-d2fc-479f-ad57-24cc5d238595 ) }} Shows button link {{ /if }} 
 {{ /user }}

{{ /user:in

{{ asset:photos}}

My problem is on the in_array modifier. If i use:

{{ if (participantes | in_array:{id} ) }} Shows button link {{ /if }} 

Statamis throws a Parse error: syntax error, unexpected ':', so how can i check if the logged in user is included on the user field for the image shown?

Answered by Peter Rainer!
>>>>>>> Answered <<<<<<<
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