Malfunction with SED

Everything works except the sed recipe, and that's a return after
"<img" as it is in the body, so where is the problem in sed?  3D and
<agent> are dummies to omit the link.

# Recipes:

:0
* B ?? ^\/<img($.*)?src.*blankpixel.*">
{ MCHECK=$MATCH }

:0
{ LOG=$MCHECK }

:0 fb
| sed 's/$MCHECK//'

# Output from LOG:

<img
src="3Dhttp://www.<agent>.com/images/blankpixel.gif/Key=3095.LZmR.V8Eyd">

Note: Detailed Document(s) and Sample(s) are more than welcome.
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*********************************************************************
Signed,
SoloCDM

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