I couldn't get the img version to work but the image widget should work, you are missing a } in it.
<$image source={{!!my_field}}/> works for me when I put https://upload.wikimedia.org/wikipedia/commons/thumb/a/ae/Indonesia_-_Lake_Toba_%2826224127503%29.jpg/1280px-Indonesia_-_Lake_Toba_%2826224127503%29.jpg into my_field. I don't think that the img shorthand works with text references. This works [img[https://upload.wikimedia.org/wikipedia/commons/thumb/a/ae/Indonesia_-_Lake_Toba_%2826224127503%29.jpg/1280px-Indonesia_-_Lake_Toba_%2826224127503%29.jpg]] but not this [img{!!my_field}] -- You received this message because you are subscribed to the Google Groups "TiddlyWiki" group. To unsubscribe from this group and stop receiving emails from it, send an email to tiddlywiki+unsubscr...@googlegroups.com. To post to this group, send email to tiddlywiki@googlegroups.com. Visit this group at https://groups.google.com/group/tiddlywiki. To view this discussion on the web visit https://groups.google.com/d/msgid/tiddlywiki/9c2c5005-119a-4d11-8845-e29c3a431064%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.