Minimum image size (separate width and height entries) options have been added to the General Options, which will allow you to decide what the smallest dimensions you want to be allowed in the slider. Both conditions must be met to allow the image to show. If either dimension is not met, this will result in the default image showing. This works for both attachments and IMG tags in the vB4 version, but only IMG tags in the vB3 version. The new options are in v1.0.7, which is now available for download.