A random assortment of images to test that covers a wide variety of formats we use (Just going to give thumbnail urls, hope that's good):

* Super large tiff file: https://upload.wikimedia.org/wikipedia/commons/thumb/3/39/Zentralbibliothek_Z%C3%BCrich_-_Mittelalterliche_Stadt_-_000005203.tif/lossy-page1-1024px-Zentralbibliothek_Z%C3%BCrich_-_Mittelalterliche_Stadt_-_000005203.tif.jpg
* Small tiff file: https://upload.wikimedia.org/wikipedia/commons/thumb/8/89/%2215th_or_16th_century_Benin_king%22_-_NARA_-_558985.tif/lossy-page1-179px-%2215th_or_16th_century_Benin_king%22_-_NARA_-_558985.tif.jpg
* large PNG file https://commons.wikimedia.org/wiki/File:Arab_West_Midlands_2011_census.png
* large full colour png file https://upload.wikimedia.org/wikipedia/commons/thumb/d/d0/Welland_cafe_inside_02.png/450px-Welland_cafe_inside_02.png
* small png https://upload.wikimedia.org/wikipedia/commons/thumb/9/98/P_sports.png/120px-P_sports.png
* Thumbnail of VP8 webm file https://upload.wikimedia.org/wikipedia/commons/thumb/d/d3/%27Trick_or_Treat%27_-_Kinetic_Typography.webm/540px--%27Trick_or_Treat%27_-_Kinetic_Typography.webm.jpg
* VP9 thumbnail: https://upload.wikimedia.org/wikipedia/commons/thumb/e/e1/VP9test.webm/512px--VP9test.webm.jpg (This doesn't work on old image scalars, I hope it works on the new one).
* ogg thumbnail: https://upload.wikimedia.org/wikipedia/commons/thumb/7/75/Reflex-Control-of-Robotic-Gait-Using-Human-Walking-Data-pone.0109959.s016.ogv/300px--Reflex-Control-of-Robotic-Gait-Using-Human-Walking-Data-pone.0109959.s016.ogv.jpg
* xcf file https://upload.wikimedia.org/wikipedia/commons/thumb/9/90/%22What_a_Brilliant_Idea!%22_Barnstar.xcf/111px-%22What_a_Brilliant_Idea!%22_Barnstar.xcf.png (Note, newer image magick has fixed a bunch of xcf bugs, this file may render differently but "better" on the new version)
* Random djvu image thrown in for good measure: https://upload.wikimedia.org/wikipedia/commons/thumb/3/3b/%27A_morte.djvu/page11-398px-%27A_morte.djvu.jpg
* PDF that is landscape oriented https://upload.wikimedia.org/wikipedia/commons/thumb/b/b0/GA20891.pdf/page1-800px-GA20891.pdf.jpg (make sure that dimensions are right)
* Animated GIF https://upload.wikimedia.org/wikipedia/commons/thumb/5/5d/Cigarette_sales_per_Capita_in_the_United_States%2C_1970_-_2012.gif/800px-Cigarette_sales_per_Capita_in_the_United_States%2C_1970_-_2012.gif
* SVG lang option - make sure https://upload.wikimedia.org/wikipedia/commons/thumb/e/e1/SystemLanguage.svg/320px-SystemLanguage.svg.png says "en" and https://upload.wikimedia.org/wikipedia/commons/thumb/e/e1/SystemLanguage.svg/langfr-320px-SystemLanguage.svg.png says "fr"
* Do the svg fonts change significantly https://upload.wikimedia.org/wikipedia/commons/thumb/4/4e/Meta_SVG_fonts.svg/1024px-Meta_SVG_fonts.svg.png (or https://upload.wikimedia.org/wikipedia/commons/thumb/d/d8/MediaWiki_SVG_font_list.svg/920px-MediaWiki_SVG_font_list.svg.png but that would be a pita to compare)
** SVGs is probably the place that's most likely to get a regression, but unfortunately I don't really know enough to give specific svg features to test.

Some other things that probably won't work, but worth testing on the off chance the update fixes the issue:

* https://upload.wikimedia.org/wikipedia/commons/thumb/3/3b/WorldAviation.198409.BackCover.pdf/page1-342px-WorldAviation.198409.BackCover.pdf.jpg (Currently doesn't work because it takes way to long to render, just curious if that changes with the new server)
* https://upload.wikimedia.org/wikipedia/commons/thumb/7/70/John_Stuart_Mill%2C_Considerations_on_Representative_Government_%281st_ed%2C_1861%29.pdf/page1-382px-John_Stuart_Mill%2C_Considerations_on_Representative_Government_%281st_ed%2C_1861%29.pdf.jpg JPEG2000 chunks in pdf files. Didn't used to work, maybe upgrade fixed?

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When are you planning to put the new server in rotation? I'd like to make an announcement on Commons:VP before that happens so that users can be on the look out for any rendering changes.