After inserting several drawings (.JPG files) into my SMath page, I was surprised to learn that I could not delete them. I can select them, move them around, but I can't delete them. When right-clicking on the image, or using the Edit Menu, "Delete" is "grayed" out. Is this a "bug", or is something that I am missing?
You can't use these options when the object (the image region) is focused (left click inside it); I think this is congruent because someone may think to delete pixels or regions of the image (however a feature not implemented).
You can delete it if you select the object (click on the canvas, hold the mouse button down an drag the pointer over the object(s)); in this case both the ways you have tried are available (context menu or "Edit" menu).
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Selecting the picture object the way you suggested, left mouse click and drag over object (object turns blue), allows me to delete it. So, just treat inserted picture blocks like text or math areas.