@Model(adaptables = {Resource.class})
public class ImageModel {
    @SlingObject
    private SlingHttpServletRequest request;

    @SlingObject
    private Resource resource;
}

@Model(adaptables = {SlingHttpServletRequest.class})

<sling:adaptTo adaptable="${slingRequest}" adaptTo="models.ImageModel" var="m"/>

@Model(adaptables =  { SlingHttpServletRequest.class, Resource.class }, defaultInjectionStrategy = DefaultInjectionStrategy.OPTIONAL)
public class ImageModel {
    @Self
    private Resource resource;

    @SlingObject
    private ResourceResolver resourceResolver;

    @SlingObject
    SlingHttpServletRequest slingRequest;
}