At your imgur images, click on an image to open it.
Ignore all the Copy options on the right, just right-click on the image itself and choose "Copy image".
Then in your forum Reply box or Message you're composing, use Ctrl+V to paste the image.
If the image is too large for the Reply box or Message, double-click on the image to open the properties. Make sure the image proportions are "locked" (little padlock icon) and put "600" or less in the "Width" box and click OK.
I resized this image to a width of 350.
Someday my cards may double in value and then be worth half of what I paid for them.