You are actually geting the image Id from the Media Folder. If am not mistaken you are using a media Picker here right? 

Yes I am using the media picker.

Try this

@{
var mediaPicker = Model.welkomImage;
if(!String.IsNullOrEmpty(mediaPicker)){

var img = Model.MediaById(mediaPicker);
 <div id="image"><img src="@img.umbracoFile"></div>
}
} 

Getting this error now,

Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately. 

Compiler Error Message: CS1061: 'Umbraco.Web.Models.RenderModel' does not contain a definition for 'welkomImage' and no extension method 'welkomImage' accepting a first argument of type 'Umbraco.Web.Models.RenderModel' could be found (are you missing a using directive or an assembly reference?)

Source Error:

Line 15:         <div class="inhoudWelkom">
Line 16:             @{
Line 17: var mediaPicker = Model.welkomImage; Line 18: if(!String.IsNullOrEmpty(mediaPicker)){
Line 19: 

found the problem, thanks for the code :)

What version of umbraco are you using  ? 

@using umbraco.MacroEngines;
@using umbraco.cms.businesslogic.media;
@using umbraco.BusinessLogic;
@inherits umbraco.MacroEngines.DynamicNodeContext 
@{
        var mediaPicker = Model.welkomImage;
        if(!String.IsNullOrEmpty(mediaPicker)){
            var img = Model.MediaById(mediaPicker);
             <div class="inhoudWelkom">           
                     <div id="image"><img src="@img.umbracoFile"></div>                
                 </div>
        }
} 

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