+> This was not a known bug before your report. It looks as though every
+> time we use `Image::Magick->Read(":foo.png")`, which is (or was)
+> ImageMagick's syntax for opening a file of unknown type without
+> interpreting a prefix containing `:` as a special directive instead
+> of part of the filename, it fails.
+>
+> Please try re-running the test with better diagnostics using
+> [commit 4ace7dbb7](http://source.ikiwiki.branchable.com/?p=source.git;a=commitdiff;h=4ace7dbb7)
+> and report what it says. --[[smcv]]
+
+>> I see the same issue on Fedora, with ImageMagic 6.9.9-19:
+>>
+>> # Failed test at t/img.t line 119.
+>> # got: 'no image: Exception 435: unable to open image `:t/tmp/out/imgconversions/10x-redsquare.png': No such file or directory @ error/blob.c/OpenBlob/2701'
+>> # expected: '10x10'
+>> [...]
+>>
+>> So it seems, that an empty coder prefix is not accepted anymore. To me it seems that [this commit](https://github.com/ImageMagick/ImageMagick/commit/4bc9b6b) changed the behavior. Unfortunately, the commit message doens't tell us about the reasons behind. The commit is included from version 6.9.8-3 on.
+
+>>> This should now be [[fixed|done]] in git and in the next release.
+>>> The test failure does not indicate a loss of functionality, unless
+>>> you are using uncommon image formats enabled with
+>>> `img_allowed_formats: [everything]`, which is a potential security
+>>> vulnerability because it exposes the attack surface of all
+>>> ImageMagick decoder modules. --[[smcv]]