Image Scaling Not Working

[POTKC]

I remembered that usually in BBCode you can put '=(width)x(height)', for example '=1200x400' into an 'img' tag to scale the image, so I typed it in like that, and instead of the image being displayed the actual text with the image link appeared. So I tried to do it the proper way, through the 'full edit' mode, put in the dimensions - and it doesn't work. If size is included in the img tag, the forum doesn't recognize it as an img tag.