Find the matrix that corresponds to projecting onto the vector $\begin{pmatrix} 1 \\ 7 \end{pmatrix}.$
From the projection formula, the projection of $\begin{pmatrix} x \\ y \end{pmatrix}$ onto $\begin{pmatrix} 1 \\ 7 \end{pmatrix}$ is
\begin{align*}
\operatorname{proj}_{\begin{pmatrix} 1 \\ 7 \end{pmatrix}} \begin{pmatrix} x \\ y \end{pmatrix} &= \frac{\begin{pmatrix} x \\ y \end{pmatrix} \cdot \begin{pmatrix} 1 \\ 7 \end{pmatrix}}{\begin{pmatrix} 1 \\ 7 \end{pmatrix} \cdot \begin{pmatrix} 1 \\ 7 \end{pmatrix}} \begin{pmatrix} 1 \\ 7 \end{pmatrix} \\
&= \frac{x + 7y}{50} \begin{pmatrix} 1 \\ 7 \end{pmatrix} \\
&= \begin{pmatrix} \frac{x + 7y}{50} \\ \frac{7x + 49y}{50} \end{pmatrix}.
\end{align*}To find the matrix for the projection, we write this vector as the product of a matrix and the vector $\begin{pmatrix} x \\y \end{pmatrix}$:
\[\begin{pmatrix} \frac{x + 7y}{50} \\ \frac{7x + 49y}{50} \end{pmatrix} = \begin{pmatrix} 1/50 & 7/50 \\ 7/50 & 49/50 \end{pmatrix} \begin{pmatrix} x \\y \end{pmatrix}.\]Thus, the matrix for this transformation is $\boxed{\begin{pmatrix} 1/50 & 7/50 \\ 7/50 & 49/50 \end{pmatrix}}.$