While any resulting cards will of course be fan productions and in no way legal or official, I still encourage everyone to source their artwork responsibly; acquire art from as close to an official source as possible so the artist’s intentions and design remain intact, connect with the artist in some way to ask permission or alert them of your use, and credit the artist on the card featuring their work (that is why the artist credit line was added!) as well as any accompanying documentation or showcase efforts.
Beyond that. some norms have arisen in the five sets WotC gave us which are worth exploring for consistency with released product and general coherence as well. The links toward the end of the article are artists, collections, and some official channels for spoiler/preview/concept art related to Transformers properties that are good sources.
Characters; The characters are almost always pulled from the files for the mobile game “Transformers Legends.” Many of the artists listed here worked on Legends and provided pieces of one stripe or another. For general consistency, use similar selections when picking artwork for characters. When working on “themed” collections, choose artwork from related collections, IE all pieces from War/Fall of Cybertron or from IDW’s ongoing series.
Battlecards; Battlecards were pulled from a variety of places, but typically from the IDW Transformers comics. When sourcing this work, look for elements from these sources but try to avoid including speech bubbles or other comic framing elements as that has a tendency to distract. Many of the listed artists have made their finished artwork available on their galleries or Deviant Art pages without text; try to defer to these before using scans of pages with text elements added.
Stratagems; ALL Stratagems officially released feature the artwork of the character card they are updating. This is a reasonable convention as it helps keep their use on the field clear. When devising new Stratagems, aim to use the artwork of the cited card first.
Sizes: Always start with the largest possible file/version of the image you can. Images can scale down relatively easily in MSE, but you will always end up with poor quality if you scale up.
When importing an image, watch the “Zoom” rating; anything greater than 100% indicates that MSE is stretching the image to fit the dimensions given which will result in worse quality. Going a little beyond 100% won’t be evident right away, but moving past 120% becomes quite clear at a quick glance that the image is low resolution.
Try to leave the settings alone, especially the size at “Size To Fit”; this is MSE automatically sizing a window proportionate to the viewing pane the image will fill. “Force To Fit” crams the whole image into the window and this can result in distortions to the artwork as something is crushed on the sides or top.
“Original Size” sets the zoom to 100% provided the artwork is bigger than the view port; it will never work on images that are too small.
“Custom Size” allows you some leeway in stretching the source selection provided the image is big enough but is not recommended.
Ken Christiansen (https://www.facebook.com/pg/The-Art-of-Ken-Christiansen-214146041944051/photos/?tab=album&album_id=906012532757395)
Dan Kahana (https://www.deviantart.com/dan-the-artguy/gallery)
Evan Gauntt (https://www.deviantart.com/zeromayhem/gallery)
Thomas Deer (https://www.deviantart.com/teyowisonte/gallery)
Eryck Webb (https://www.deviantart.com/eryckwebbgraphics/gallery)
Josh Perez (https://www.deviantart.com/dyemooch/gallery)
Agni Interactive (https://agniinteractive.carbonmade.com/projects/5248590#1)
Casey Coller (https://www.deviantart.com/caliber316/gallery )
Alex Milne (https://www.deviantart.com/markerguru/gallery)
Marcelo Matere (https://www.deviantart.com/marcelomatere/gallery)
Liam Shalloo (https://www.deviantart.com/liamshalloo/gallery)
Jason Cardy (https://www.deviantart.com/jasoncardy/gallery)
Joana Lafuente (https://www.deviantart.com/khaamar/gallery)
Andrew Griffith (https://www.deviantart.com/glovestudios
Transformers Legends Collections