problem in: img_options["size"] = img_size

you can't use the 'size' option with the tag helper, only with the
image_tag helper. the "size" option will get translated to
height/width with image_tag

with the tag helper, you have to give all the correct attributes, so
use height/width options.

img_options["height"], img_options["width"] = img_size.split("x")