It seems that some changes on the Tibia Wiki side caused the problems. I compared the URLs of the images from the past and current URLs and noticed a difference:
Previous: https://vignette.wikia.nocookie.net/tibia/images/e/e1/Cluster_of_Solace.gif/revision/latest/scale-to-width-down/32?cb=20131204024157&path-prefix=en
Now: https://static.wikia.nocookie.net/tibia/images/e/e1/Cluster_of_Solace.gif/revision/latest/scale-to-width-down/32?cb=20131204024157&path-prefix=en
Changing static to vignette in the image URLs manually seems to be workaround that helps.
Please note, however, that the recommended way to add images is always to upload them! Images referenced by URL can stop working at any time (dependency on the server they are located on) and cause your question/answer to take longer to load since there's a need to fetch resources from an external server.