staticImageViewer.cmp

<aura:component implements="force:appHostable,flexipage:availableForAllPageTypes,flexipage:availableForRecordHome,force:hasRecordId,forceCommunity:availableForAllPageTypes,force:lightningQuickAction" access="global" >
    <aura:attribute name="imgUrl" type="string" required="true" default="https://farm8.staticflickr.com/7683/17369785125_efca0c32ec_o.jpg"/>        
    <img src="{!v.imgUrl}" />
</aura:component>

staticImageViewer.css

img.THIS {
   width:100%; 
}

staticImageViewer.design

<design:component >
    <design:attribute name="imgUrl" label="Image Url" description="url for where the image lives"/>
</design:component>