Try using:
dmx-bind:src="ArticleImageURL ? '/images/articles/'+ArticleImageURL : '/images/apple-icon-72x72.png'"
Or
dmx-bind:src="ArticleImageURL != '' ? '/images/articles/'+ArticleImageURL : '/images/apple-icon-72x72.png'"
Try using:
dmx-bind:src="ArticleImageURL ? '/images/articles/'+ArticleImageURL : '/images/apple-icon-72x72.png'"
Or
dmx-bind:src="ArticleImageURL != '' ? '/images/articles/'+ArticleImageURL : '/images/apple-icon-72x72.png'"