U+FE0F is the Unicode variation selector commonly used to request emoji presentation.
This character is named VARIATION SELECTOR-16, or VS16. When it follows a character that can have either text or emoji presentation, it generally signals that the character should be rendered as a colorful emoji. For example, U+2764 followed by U+FE0F produces the familiar red-heart presentation on many systems.
The selector is invisible by itself and does not represent a picture. It modifies the presentation of the preceding character. The related U+FE0E, VARIATION SELECTOR-15, generally requests text presentation instead.
Variation selectors are often confused with zero width joiners. A variation selector changes presentation, while U+200D joins multiple emoji characters into a single grapheme sequence, such as a family or profession emoji. Actual display still depends on the operating system and font.