Learn Spanish (Latin America): Tú tienes una foto de México.

The word foto is actually short for fotografía. Because fotografía is a feminine word (it ends in "a"), its short version foto keeps that feminine gender. That is why we use the feminine word for "a" (una) instead of the masculine un.

Do I need to include Tú in this sentence, or can I just say Tienes?

You can absolutely just say Tienes una foto de México. In Spanish, the verb form tienes already tells us that "you" are doing the action, so the pronoun tú is optional. People usually include tú when they want to add emphasis, like "You have a photo of Mexico (and I don't)."

Why does Tú have an accent mark here?

The accent mark helps tell two identical-sounding words apart in writing. Tú (with the accent) is the subject pronoun meaning "you," which is what we need here. Tu (without the accent) is a possessive word meaning "your" (as in tu foto, meaning "your photo").

How is the "x" in México pronounced?

In the word México, the "x" is pronounced like a strong, raspy English "h" sound (very similar to the Spanish "j"). It is not pronounced with the "ks" sound we use in the English word "Mexico."