Please always post usable documents including all macros defined, not just fragments.
You can scale the image and text together:
\documentclass{article}
\usepackage{overpic,color}\def\bv{b_v}
\begin{document}
\begin{overpic}[scale=0.3]{example-image-a}
\put(-9,69){\color{black}\vector(0,1){12}}
\put(-10,82){$\hat{z}$}
\put(-9,68){\color{black}\vector(0,-1){12}}
\put(-11,51){$\hat{v}$}
\put(-63,-1){$\theta$}
\put(-115,44){$\partial_s\theta$}
\put(-1.5,92){$q$}
\put(88,-0.5){$|\bv|$}
\put(-1,-0.5){$T$}
\end{overpic}
\vfill
\hrule
\vfill
\scalebox{.2}{%
\begin{overpic}[scale=0.3]{example-image-a}
\put(-9,69){\color{black}\vector(0,1){12}}
\put(-10,82){$\hat{z}$}
\put(-9,68){\color{black}\vector(0,-1){12}}
\put(-11,51){$\hat{v}$}
\put(-63,-1){$\theta$}
\put(-115,44){$\partial_s\theta$}
\put(-1.5,92){$q$}
\put(88,-0.5){$|\bv|$}
\put(-1,-0.5){$T$}
\end{overpic}}
\vfill
\hrule
\vfill
\scalebox{2}{%
\begin{overpic}[scale=0.3]{example-image-a}
\put(-9,69){\color{black}\vector(0,1){12}}
\put(-10,82){$\hat{z}$}
\put(-9,68){\color{black}\vector(0,-1){12}}
\put(-11,51){$\hat{v}$}
\put(-63,-1){$\theta$}
\put(-115,44){$\partial_s\theta$}
\put(-1.5,92){$q$}
\put(88,-0.5){$|\bv|$}
\put(-1,-0.5){$T$}
\end{overpic}}
\end{document}
Best Answer
As I suggested in my comment of 6 months ago, the
\stackinset
macro of thestackengine
package provides this capability. You might consider it an alternative tooverpic
if you want positioning relative to the local figure.