A few months ago, we made a change to the template editor. The result was a gray ‘REPLACE’ placeholder box being displayed when the <$imagesrc$>
tag was present within a repeater, but no default image had been defined. Initially, we thought that this would make it easier to see where images could be added to a template, however based on your feedback, it seems that the change created a fair amount of confusion.
So as part of our recent update, we’ve gone back to how things were done before. Instead of clicking on a gray ‘REPLACE’ placeholder image, you can add an image to a repeater by clicking ‘Insert an image’ from within the template content editor:

Note that this is only valid if you have added the <$imagesrc$>
tag to a repeater within your template.
Many thanks to everyone who sent in their feedback regarding the template editor. Sometimes, the journey towards improving things involves taking a step in the opposite direction!