Before making your contribution, please read the following recommendations.
Each image should be with PNG or GIF extension and have sharp edges (look like pixel art). You can achieve this effect in Photoshop by scaling your image to 300% with neighbor color setting applied.

It is also recommended to mind image standard sizes that are used in the game.

Standard Sizes Table

Type | Initial | Final
Character portrait | 32 px | 96 px
Item icon | 18 px | 54 px
Map object | 16 px | 32 px
Encounter image | 64 px | 192 px
Location animation | 240x137 px | 720x411 px
Cutscene animation | 320x200 px | 960x600 px

If your image doesn't match the standards, most likely, it won't be published.