Tax implications with joint checking accounts

Any interest paid to the account will be reported by the one whose social security number is on the account. 

@AndrewA87 if either or both of you are paying tax-deductible expenses, keep those receipts because if you are ever audited, the IRS may ask for proof that the expense is really yours and not the other party's. The same for deposits. This is totally at the discretion of the IRS auditor (or even the state auditor if you have state income taxes) 

If one of the owners deposits money into the joint account is that considered taxable income for the other owner of the joint account?

No, that’s not income to the other person but if the amount is substantial it could be considered a gift. 

Thanks for the quick response.

Would it only be considered a gift if the person who did not make the substantial deposit withdrew the money from the joint account or is it considered a gift by just being deposited into the joint account?

As soon as the other person has the ability to withdraw the money it is a gift.