On Windows you can just drag and drop image file(s) into the forum post edit box.
(Moving to the Ruby API category.)
Testing the landing page for:
https://www.bimandco.com/en
The images load fine in MSIE v11 outside of SketchUp.
They load fine inside a SketchUp webdialog in SketchUp 2016, with browser emulation set to IE9, Win7 (with latest v11 installed and updated.) But your page can override that setting.
d = UI::WebDialog::new("Test")
d.set_url( "https://www.bimandco.com/en" )
d.show