I think I may have suggested this before, but here is a good way to implement custom guild emblems:
All guilds start with a base template consisting of the shield picture; they have and a few common symbols at their disposal. These symbols have the option of being scaled to one of 3 or 4 sizes, placed on the base template (grid based), mirrored, rotated in 90 degree increments, or recolored.
The design canvas would have an inner square representing the maximum size of the guild emblem (anything outside this square will be chopped off); the base template allows you to further customize the shape of your emblem by chopping it off into the shape of a shield, for example.
This allows a finite but huge number of combinations, but can be stored as a list of elements (symbol ID, scale factor, mirror, rotation, X, Y, color) rather than as an unwieldy bitmap or image. As you buy guild wings, you automatically get a few new symbols and base templates; it also unlocks additional symbols for purchase from the Birdsong Emporium.

Initial allotment:
"Shield" base template
6 colors (red, green, blue, orange, yellow, purple)
6 standard symbols for generic armor, helm, shield, bomb, gun and sword

Additionally available (some would be unlocked at wing purchase, others would need to be purchased separately)
"Star", "Circle" base templates (can't think of many good shapes)
Full color palette
All equipment icons
Miscellaneous icons (like social, arsenal, energy, crown, etc.)
Status effect icons (fire, shock, etc.)
Monster family icons
...and more